The cdio API always reads in sectors (fixed CDIO_CD_FRAMESIZE_RAW
blocks). In the past, mpv/MPlayer streams had a way for a stream to
signal a sector size, so the stream's fill_buffer implementation could
ignore the length argument. Later, that was removed, but stream_cdda.c
was left with assuming that the read size was always larger than the
sector size (rightfully at the time). Even later, this assumption was
broken with commit f37f4de, when it was suddenly possibly that smaller
reads were performed (at ring buffer boundaries). It returned EOF if the
buffer size was too small, so playback stopped very early.
Fix this by explicitly handling arbitrary sizes.
Tested with a .cue/.bin file only.
Fixes: #7384
f304a79935