I18n: Update translation ast (63%).

28 translated messages, 16 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation ast (63%).

28 translated messages, 16 untranslated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
I18n: Update translation fr (100%).

44 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).
Fix setting internal error to NULL in pixbuf thumbnailer (bug #10878)
Enable support for video/webm in ffmpeg thumbnailer plugin (bug #10360)

Patch provided by kwiatek@iv.pl.
Revert "Fix setting internal error to NULL in pixbuf thumbnailer (bug #10878)"

This reverts commit dc74b5d38009a5f6c1064f69d8b7d632ae0b52a5.
Add comments for the previous revert.