BUG: Raise ValueError with nan in timeaware windows
- [x] closes #34617
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Raising a ValueError when NaN is in timeaware window.

cc @mroeschke 