Thumbbar now with less flickering.


git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@1028 ef8490bc-f317-4725-81ed-e95a9aca1bcf
Fix get thumbnail exception.

From: Benoit Pierre <benoit.pierre@gmail.com>

git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@1029 ef8490bc-f317-4725-81ed-e95a9aca1bcf