avformat: Enforce one-stream limit where appropriate

Several muxers (e.g. pcm muxers) did not check the number
of streams even though the individual streams were not
recoverable from the muxed files. This commit changes
this by using the FF_OFMT_MAX_ONE_OF_EACH flag
where appropriate.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavformat/bit.c

@@ -167,6 +167,8 @@ const FFOutputFormat ff_bit_muxer = {
     .p.extensions   = "bit",
     .p.audio_codec  = AV_CODEC_ID_G729,
     .p.video_codec  = AV_CODEC_ID_NONE,
+    .p.subtitle_codec = AV_CODEC_ID_NONE,
+    .flags_internal   = FF_OFMT_FLAG_MAX_ONE_OF_EACH,
     .write_header = write_header,
     .write_packet = write_packet,
 };