avformat/mov: Check channels for mov_parse_stsd_audio()

Fixes: signed integer overflow: -776522110086937600 * 16 cannot be represented in type 'long'
Fixes: 40563/clusterfuzz-testcase-minimized-ffmpeg_dem_MOV_fuzzer-6644829447127040

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg


Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 3a64a4c5)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>