Don't set sd->video to NULL. sd->video is initialized only when

Don't set sd->video to NULL. sd->video is initialized only when
emotion_object_init() is called. Hence, setting sd->video to NULL
there implied that the code:

emotion_object_init(o, module);
emotion_object_file_set(o, file1);
emotion_object_file_set(o, NULL);
emotion_object_file_set(o, file2);

seg fault.

(such code is useful when you want to reset the same stream
(file1 = file2). The other solution would be to destroy everything
and recreating the pipeline, which is not nice)

git-svn-id: http://svn.enlightenment.org/svn/e/trunk/e17/libs/emotion@34571 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33