BUG: GH25495 incorrect dtype when using .loc to set Categorical value for column in 1-row DataFrame
- [x] closes https://github.com/pandas-dev/pandas/issues/25495
- [x] 1 test added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`


> lgtm. can you add a whatsnew note in bug fixes / indexing section. ping on green.

Thanks @jreback. Added a whatsnew note.  Hello @keechongtan! 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 2020-01-27 11:52:36 UTC > lgtm. can you merge master & ping on green.

@jreback, merged master and all tests passed if you can merge master and update would be great @keechongtan if you'd rebase once more we can merge. ping when green. thanks @keechongtan 

happy to have a followup as discussed (pls create an issue) @jreback seems like this wasn't backported.

@MeeseeksDev backport 1.0.x