fixed: We should only run that code when called from the thumbloader

This should fix @da-anda's problem mentioned here https://github.com/xbmc/xbmc/commit/a7e0f723c5d28b670079dd6f3be9def818fc22e4#commitcomment-5708369 . It should fix the regression caused by https://github.com/xbmc/xbmc/commit/ce284f8