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>```
My issue here is that I struggle to remember what the conditions are for when we need to insert a BR, and I have to reverse engineer this if statement to understand them. We decided to leave it how it is because we couldn't agree!