avformat/mvdec: Do not set invalid sample rate

Fixes: signed integer overflow: -682581959642593728 * 16 cannot be represented in type 'long'
Fixes: 37883/clusterfuzz-testcase-minimized-ffmpeg_dem_MV_fuzzer-5311691517198336

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

@@ -156,9 +156,10 @@ static int parse_audio_var(AVFormatContext *avctx, AVStream *st,
     } else if (!strcmp(name, "NUM_CHANNELS")) {
         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)
+        int sample_rate = var_read_int(pb, size);
+        if (sample_rate <= 0)
             return AVERROR_INVALIDDATA;
+        st->codecpar->sample_rate = sample_rate;
         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;