lib: fix signaling frames ready to be returned when no frame delay is expected
lib: fix signaling frames ready to be returned when no frame delay is expected

Prevents dav1d_get_picture() from returning EAGAIN when no frame delay was
requested (threads=1, or threads > 1 and max_frame_delay=1).

Signed-off-by: James Almer <a1bd7e8a8c5f39f027618398c9ca41dd2205b55b@gmail.com>

videolan/dav1d