BUG: read_html with a single column table #9178
This commit fixes a crash on read_html(html, flavor="bs4") if table only has one column.

closes #9178 

pls add a test
 Please add a test
 The test should probably test that if it succesfully parses one column table but in which file should I put it? I've never written nose tests.
 Usually tests go in the tests sub-directory and in the module you want to test.  For example, you should put your test in `pandas.io.tests.test_html`.  And in there probably add a test in the `TestReadHtml` class.  There are plenty of examples there to get you started.  And then you can run your test using nosetests (you probably just want to run the module: `nosetests pandas.io.tests.test_html`).
 @boarpig needs a test.
 @boarpig this needs a test pls.
 @boarpig pls add a test
 closing, if/when updated pls reopen
 I have just encountered this bug in 0.18 and the fix from this PR fixed that. Is the only limiting factor to merge this PR adding tests? I could probably do it (and will appreciate any help).
 yep needs tests
 But I can see there are already tests for this part [here](https://github.com/pydata/pandas/blob/827745dcf0cec55e8b071acc54b0aa5e610e640e/pandas/io/tests/test_html.py). What else should be added? This change seems to be sufficiently tested by current tests. Thanks
 I am willing to finish this, but I need an answer to the previous post. 
 you need to replicate the example in the issue - that is the test
 I have done it in a [new PR](https://github.com/pydata/pandas/pull/12975) (so I don't have to do a rebase).
