Orphan <br> should be transformed into <p><br></p>

[Frederico Caldeira Knabben]

We do several inline elements fixing that are found orphan inside body. This was true for <br> as well, until we reverted a fix that was causing #9167.

Because of that, I've commented out a test made for that case form dt/core/htmlparser/fragment.html, test name "test_parser_13".

It is still unclear for me the cases for this fix, but considering that we were used to do so, we should keep doing it.

I'm just unsure if this is necessary.