Steps to Reproduce

1. Open a page containing RadEditor with some content in it
2. In Design mode, select all text (Ctrl+A)
3. Delete the selected text
4. Switch to HTML mode
5. Switch back to Design mode
6. Press Ctrl+Z (Undo) a couple of times.
   

• A JavaScript error is thrown in the browser console
• The undo operation fails to restore the deleted content
• Error occurs in _updateBrowserRangeStart method when calling this.range.setStart(e, t)

Expected Result

• The undo operation should work without errors
• The previously deleted text should be restored
• No JavaScript errors should appear in the console