plugins/selection js error on destroy

Hi,

I'm using CKEditor for an app that has to create and destroy instances multiple times.

Reproduction steps:
1. Data in editor has been changed
2. editor.updateElement() was called
3. editor was destroyed
4. editor was re-created

Got a JS error message originating in plugins/selections/plugin.js:229

To resolve added verification that .getSelection() has value:

var selection = doc.$.defaultView.getSelection();
selection && selection.setPosition( fillingChar.$,fillingChar.getLength() );