IE7 - Nesting unordered lists within ordered lists crashes IE7

[ischerer]

Steps to Reproduce

1. In the editor, type the following:
   
   Line 1
   Line 2
   Line 3
   
   
2. Highlight all three lines of text, click the "Insert/Remove Numbered List" button.
3. Highlight "Line 2", click the "Insert/Remove Bulleted List" button.

Expected Result
Text has styles successfully applied.

Actual Result
Pressing "Insert/Remove Bulleted List" will cause IE7 to crash.

Note: This will also occur if you attempt to nest an ordered (numbered) list into an unordered (bulleted) list.

[Jakub Ś]

DUP of #8281