BUG: Fix window aggregations to skip over unused elements (GH-45647)
- [x] closes #45647
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit) for how to run them
- [x] whatsnew entry

add a whatsnew to 1.4.1 in the bug fix section https://github.com/pandas-dev/pandas/blob/main/doc/source/whatsnew/v1.4.1.rst small comment @mroeschke good here? thanks @rtpsw 