JS error is thrown when replacing page break and IE

[Sa'ar Zac Elias]

To reproduce

• Open an empty CKEditor instance and insert 2 page breakes.
  
• SELECT (drug the selection - not by clicking on a page break sign) the 2 page breakes signs (make sure you are not selecting any other thing - including text nodes, this is important).
  
• Insert an element on it (HR for example).

JS error is thrown (getFirst() is empty or not an object).

[Jakub Ś]

Issue is reproducible in all browsers. It's hard to get same results as it's hard to select those two pagebreaks with a mouse.

I have got the best result when inserting the below code:

<div style="page-break-after: always;">
	<span style="display: none;">&nbsp;</span></div>
<div style="page-break-after: always;">
	<span style="display: none;">&nbsp;</span></div>

When selected two page breaks and pressed horizontal line button all browsers returned:

Message: 'type' is null or not an object/ Cannot read property 'type' of null/ startNode is null
Line: 1530
URI: /3.6.2/ckeditor/_source/core/dom/range.js

The above result is consistent for all browsers from CKEditor 3.6.1 rev [6963]

Before this revision results where different: Either horizontal button (or any button) had no result on content when pressed or worked or the error was slightly different.

Anyway the first error I have managed to get occurred in CKEditor 3.0.2 in Firefox browser: FF 3.1
Message: parentNode is null
URI: /3.1/ckeditor/_source/core/dom/node.js
Line: 197