lavf/segment: do not copy codec_tag when not available

lavf/segment: do not copy codec_tag when not available

Some muxers do not allow stream if codec_tag is incompatible.

Sometimes the passed input codec's codec_tag is not compatible with the
output muxer.

Because the codec_tag field of the segment muxer cannot be set, ffmpeg.c
doesn't know how to handle these cases.

Signed-off-by: ChanMin Kim <kcm1700@gmail.com>
Signed-off-by: Stefano Sabatini <stefasab@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>