BUG: pd.crosstab(s1, s2) handle column index incorrectly when both series have tuple names
- [ ] closes #18321
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

ping @jreback  Thanks @charlesdong1991 