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>```
node has no child element
AND
node's text content when trimmed is empty
AND
is not a void-element

I think the code is pretty easy to read.