Don't wait until later, we want to know here if the codec can be opened or not
for the requested format. This was removed (accidentially?) by
119e09eac315f79ac2cf45b4441ad1d932130614
Without this decodebin has no way to switch to a different decoder if this one
does not work.
https://bugzilla.gnome.org/show_bug.cgi?id=762613