Ensure selectable container fix

This fixes the issue when inserting a node with a child node but no text content, a```BR``` is added to the wrong place.
E.g. ```<p><b></b></p>``` => ```<p><b></b><br></p>``` when it should be ```<p><b><br></b></p>```
> <blockquote></blockquote> (albeit not great to start with, will become <blockquote><br></blockquote>) -- previously we only inserted BRs within Ps and LIs?

Yes. Is this expected? Without the BR, you couldn't select it.

This should never happen because in block mode, you always have a P element.