BUG: rolling mean and sum not numerical stable for all nan window
- [x] closes #41053
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [x] whatsnew entry

The problem is not numerical stable, so we are dividing -3e-18 / 0, which returns -inf running into line 177 setting to 0. Checking for nobs > 0 would solve these cases

cc @mroeschke 