BUG: Don't raise on value_counts for empty Int64
- [ ] closes #33317
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

thanks @dsaxton 

we don't have a full fledged ExtensionIndex yet so anytime an EA is set-index its object