avformat/mvdec: Check sample rate in parse_audio_var()

Fixes: signed integer overflow: -635424002382840000 * 16 cannot be represented in type 'long'
Fixes: 33612/clusterfuzz-testcase-minimized-ffmpeg_dem_MV_fuzzer-5704741108711424

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

@@ -157,6 +157,8 @@ static int parse_audio_var(AVFormatContext *avctx, AVStream *st,
         return set_channels(avctx, st, var_read_int(pb, size));
     } else if (!strcmp(name, "SAMPLE_RATE")) {
         st->codecpar->sample_rate = var_read_int(pb, size);
+        if (st->codecpar->sample_rate <= 0)
+            return AVERROR_INVALIDDATA;
         avpriv_set_pts_info(st, 33, 1, st->codecpar->sample_rate);
     } else if (!strcmp(name, "SAMPLE_WIDTH")) {
         uint64_t bpc = var_read_int(pb, size) * (uint64_t)8;