[IE] : Undo add extra space at the end of list item

[Garry Yao]

1. Load the editor with the following content:

   <ul>
   	<li>foo
   		<ul>
   			<li>bar</li>
   		</ul>
   	</li>
   </ul>
   

2. Make any small change then undo once;

• Actual : One unwanted whitespace is added to the end of the first list item (foo), this can be verified only in wysiwyg mode by moving cursor at the end of the list item;
• Expected: Content is reverted into the original status.

[Jakub Ś]

Reproducible in IE6-8 from CKEditor 3.0 (IE9 works fine)