avcodec/cavsdec: Check sym_factor

Fixes: runtime error: signed integer overflow: 25984 * 130560 cannot be represented in type 'int'

Fixes: 1404/clusterfuzz-testcase-minimized-5000441286885376

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 279420b5a6)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/cavsdec.c

@@ -1031,6 +1031,10 @@ static int decode_pic(AVSContext *h)
     h->scale_den[1] = h->dist[1] ? 512/h->dist[1] : 0;
     if (h->cur.f->pict_type == AV_PICTURE_TYPE_B) {
         h->sym_factor = h->dist[0] * h->scale_den[1];
+        if (FFABS(h->sym_factor) > 32768) {
+            av_log(h->avctx, AV_LOG_ERROR, "sym_factor %d too large\n", h->sym_factor);
+            return AVERROR_INVALIDDATA;
+        }
     } else {
         h->direct_den[0] = h->dist[0] ? 16384 / h->dist[0] : 0;
         h->direct_den[1] = h->dist[1] ? 16384 / h->dist[1] : 0;