Inline style incorrect when reaching document end

[Garry Yao]

Infected by [3353], apply inline style throw JavaScript Error when reaching the end of document.

Reproducing Procedures

1. Open the replace by class example page in Firefox.
2. Clear all content and insert text 'bold';
3. Click 'SelectAll' then apply 'Bold' style;
4. Double click the bold text 'bold', and Click on 'Italic' command.
   • Actual Result: JavaScript error occurred.

[Martin Kou]

Tidied up the ticket description.

[Garry Yao]

Fixed with [3395].