shorten: fix end-of-stream decoding.

enable CODEC_CAP_DELAY to flush any remaining frames in the buffer.

Stop decoding when the FN_QUIT command is found so that a trailing seek table
isn't decoded as a normal frame.

decode all channels in the same call to avcodec_decode_audio3() so that
decoding will not stop after the first channel of the last frame.

Updated FATE reference. More valid audio is now decoded.
