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>```
There are two tests that sets the content to ```<o><img></p>``` and ```<p><br></p>``` which shows that it's not going to add a ```BR``` to the ```IMG``` and ```BR```