BUG/TST: Fillna limit Error Reporting
fillna method was not throwing an ValueError with a dataframe full of
integers (no NAs) and limit keyword set to a negative number. Issue can
be seen in GH27042.

Begun with writing tests for checking the behaviour of fillna
and values of limit in test/frame/test_missing.py for both negative and
non-integer values of limit.

Then wrote new test file tests/util/test_validate_fillna_kwargs.py,
where the function would now also take limit as an argument and
perform necassary checks in there.

Made changes to util/_validators.py to correctly check values of limit
as was already done in core/internal/blocks.py

Updated calls to validate_fillna_kwargs in various files
to include the limit argument.

- [x ] closes #27042 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x ] whatsnew entry

Hello @Inevitable-Marzipan! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



















There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-06-27 14:19:09 UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=h1) Report
> Merging [#27074](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e9555159afd8caabc88b45ca6c06a16efe2f6afc?src=pr&el=desc) will **decrease** coverage by `50.17%`.
> The diff coverage is `38.46%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/27074/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #27074       +/-   ##
===========================================
- Coverage   92.04%   41.86%   -50.18%     
===========================================
  Files         180      180               
  Lines       50714    50715        +1     
===========================================
- Hits        46679    21234    -25445     
- Misses       4035    29481    +25446
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.86% <38.46%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `52.36% <ø> (-42.79%)` | :arrow_down: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `58.98% <0%> (-40.45%)` | :arrow_down: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `41.79% <0%> (-56.14%)` | :arrow_down: |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `41.73% <0%> (-54.2%)` | :arrow_down: |
| [pandas/core/arrays/numpy\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL251bXB5Xy5weQ==) | `41.28% <0%> (-53.22%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `38.45% <100%> (-55.75%)` | :arrow_down: |
| [pandas/util/\_validators.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3ZhbGlkYXRvcnMucHk=) | `35.35% <50%> (-61.46%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/gcs.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2djcy5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| ... and [139 more](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=footer). Last update [e955515...ee72cd7](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=h1) Report
> Merging [#27074](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/e9555159afd8caabc88b45ca6c06a16efe2f6afc?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/27074/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #27074      +/-   ##
==========================================
- Coverage   92.04%   92.03%   -0.01%     
==========================================
  Files         180      180              
  Lines       50714    50715       +1     
==========================================
- Hits        46679    46677       -2     
- Misses       4035     4038       +3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.67% <100%> (ø)` | :arrow_up: |
| #single | `41.86% <38.46%> (-0.1%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `95.13% <ø> (-0.02%)` | :arrow_down: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `99.43% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/datetimelike.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2RhdGV0aW1lbGlrZS5weQ==) | `97.92% <100%> (ø)` | :arrow_up: |
| [pandas/util/\_validators.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3ZhbGlkYXRvcnMucHk=) | `96.96% <100%> (+0.16%)` | :arrow_up: |
| [pandas/core/arrays/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2NhdGVnb3JpY2FsLnB5) | `95.92% <100%> (ø)` | :arrow_up: |
| [pandas/core/arrays/numpy\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL251bXB5Xy5weQ==) | `94.49% <100%> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `94.2% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `88.88% <0%> (-11.12%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `96.89% <0%> (-0.12%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/27074/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `90.94% <0%> (+0.1%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=footer). Last update [e955515...c9c39c4](https://codecov.io/gh/pandas-dev/pandas/pull/27074?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 closing in favor of #27077 