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>```
That's the difference:

``` js
var a1 = document.createElement('div'); a1.appendChild(document.createTextNode('foo'));
a1.children;
a1.childNodes;
```

Good to know! :smile: