merge SVN commit 1021337 by winterz:

add a crash guard in selectedSernums() that seems to help fix
the following part of kolab/issue3833

1. Create imap folder
2. Copy some mails in it
3. Sync
4. Create fav.
5. Rename folder
6. Sync
7. Click on a mail

svn path=/tags/kdepim/enterprise35.0.20090907.1020969/kdepim/; revision=1021341