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>```
Your current if statement is "Has no child elements AND has whitespace AND can have children". Should it be "(Has no child elements OR has whitespace) AND can have children"?

It would be nice if the code was self-documenting:

``` js
if ((nodeHasNoChildren || nodeHasWhitespace) && nodeCanHaveChildren) {…}
```