BUG: np array indexer modifed in iloc
- [ x ] closes #20852 
- [ x ] tests passed
- [ x ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
Pls implement a test for this. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21867?src=pr&el=h1) Report
> Merging [#21867](https://codecov.io/gh/pandas-dev/pandas/pull/21867?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/365eac4d27353693a2b758c87fc4bceabb74817f?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21867/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/21867?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21867      +/-   ##
==========================================
+ Coverage   91.91%   91.91%   +<.01%     
==========================================
  Files         164      164              
  Lines       49992    49993       +1     
==========================================
+ Hits        45951    45952       +1     
  Misses       4041     4041
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <100%> (ø)` | :arrow_up: |
| #single | `42.16% <0%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21867?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/21867/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `93.73% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21867?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/21867?src=pr&el=footer). Last update [365eac4...4ce3a47](https://codecov.io/gh/pandas-dev/pandas/pull/21867?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Hello @ydovzhenko! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on July 13, 2018 at 19:38 Hours UTC thanks @ydovzhenko 