viewer: fix .desktop category.
viewer: fix .desktop category.

AnilRamachandran/aravis,AravisProject/aravis,AnilRamachandran/aravis,AravisProject/aravis,AravisProject/aravis,AravisProject/aravis,AnilRamachandran/aravis,AnilRamachandran/aravis,AravisProject/aravis,AnilRamachandran/aravis