TST: Test empty input for read_csv (#14867)
 - [x ] closes #14867
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master | flake8 --diff``
 - [ ] whatsnew entry

LMK if it would be more suitable in a different test file.
## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14920?src=pr) is 84.64% (diff: 100%)
> Merging [#14920](https://codecov.io/gh/pandas-dev/pandas/pull/14920?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will increase coverage by **<.01%**

```diff
@@             master     #14920   diff @@
==========================================
  Files           144        144          
  Lines         51016      51016          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits          43184      43185     +1   
+ Misses         7832       7831     -1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [3ccb501...46ad2a2](https://codecov.io/gh/pandas-dev/pandas/compare/3ccb50131b698bccee21780c660a70bed87396d0...46ad2a2b325132234221c1bb57b6d421850a00f8?src=pr) Removed the extra test, all good now. thanks!