lavfi/vf_overlay: check that filter_frame does not return EAGAIN.

EAGAIN is used internally in the code; it currently does not make
sense as a return code from the next filter.

Should fix CID966655.
vorbisdec: Check bark_map_size.

This fixes potential divisions by zero and out of array accesses.

Reported-by: Dale Curtis <dalecurtis@chromium.org>
Found-by: inferno@chromium.org
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>