fix for read_html with bs4 failing on table with header and one column
- [x] closes [#9178](https://github.com/pydata/pandas/issues/9178)
- [x] The test is added and passing (while failing before the fix).
- [x] passes `git diff upstream/master | flake8 --diff`
- [x] whatsnew entry

Fix as had been proposed in [PR 9194](https://github.com/pydata/pandas/pull/9194#issuecomment-209849563), but this PR was closed because of tests missing. They are added now.
