[IE11] Exception when pasting page break into table

[Marek Lewandowski]

1. open any sample with CKEditor table plugin (i.e. samples/replacebyclass.html)
2. switch to source mode, and use following source code:

   <div style="page-break-after: always;"><span style="display:none">&nbsp;</span></div>
   <table border="1" cellpadding="1" cellspacing="1" style="width:500px">
   	<tbody>
   		<tr>
   			<td>
   			<p>aa</p>
   
   			<p>bb</p>
   			</td>
   			<td>&nbsp;</td>
   		</tr>
   		<tr>
   			<td>&nbsp;</td>
   			<td>&nbsp;</td>
   		</tr>
   	</tbody>
   </table>
   

3. switch back to wysiwyg mode
4. copy page break into first (top left) table cell

Expected result:
Operation should not cause exception.

Current result:
Exception is being thrown:

SCRIPT5007: Unable to get property 'isBlock' of undefined or null reference
File: ckeditor.js, Line: 323, Column: 45