avformat/mvdec: Sanity check SAMPLE_WIDTH

Fixes: signed integer overflow: 999999999 * 8 cannot be represented in type 'int'
Fixes: 30048/clusterfuzz-testcase-minimized-ffmpeg_dem_MV_fuzzer-5864289917337600

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mvdec.c

@@ -159,7 +159,10 @@ static int parse_audio_var(AVFormatContext *avctx, AVStream *st,
         st->codecpar->sample_rate = var_read_int(pb, size);
         avpriv_set_pts_info(st, 33, 1, st->codecpar->sample_rate);
     } else if (!strcmp(name, "SAMPLE_WIDTH")) {
-        st->codecpar->bits_per_coded_sample = var_read_int(pb, size) * 8;
+        uint64_t bpc = var_read_int(pb, size) * (uint64_t)8;
+        if (bpc > 16)
+            return AVERROR_INVALIDDATA;
+        st->codecpar->bits_per_coded_sample = bpc;
     } else
         return AVERROR_INVALIDDATA;