Fix for Bug 141580: Changing file association prevents thumbnail generation

["Nickolay V. Shmyrev" <nshmyrev yandex ru>]

Hello.

Description of Problem:
After specifying something else as default, or
just adding another entry to the "Open With" menu
entry it refuses to generate thumbnails for that
filetype later on. Already generated thumbnails
display just fine though.


Please, review and commit patches to fix bug #141580 in bugzilla.

								Thanks.