BUG: Added checks for NaN in __call__ of EngFormatter
- [x] closes #11981 
- [x] tests added / passed
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Closes #11981

Updated the v0.18.2 document

In the function `__call__` of EngFormatter check if decimal input is NaN.
