player: let frontend decide whether to use cover-art mode

Essentially, this lets video.c decide whether to consider a video track
cover art, instead of having the decoder wrapper use the lower level
sh_stream flag.

Some pain because of the dumb threading shit. Moving the code further
down to make some of it part of the lock should not change behavior,
although it could (framedrop nonsense).

This commit should not change actual behavior, and is only preparation
for the following commit.

0 files changed, 0 insertions, 0 deletions