westwood_aud: prevent division by zero

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
(cherry picked from commit bc7e128a6e)
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavformat/westwood_aud.c

@@ -164,6 +164,12 @@ static int wsaud_read_packet(AVFormatContext *s,
         if (ret != chunk_size)
             return AVERROR(EIO);
 
+        if (st->codecpar->channels <= 0) {
+            av_log(s, AV_LOG_ERROR, "invalid number of channels %d\n",
+                   st->codecpar->channels);
+            return AVERROR_INVALIDDATA;
+        }
+
         /* 2 samples/byte, 1 or 2 samples per frame depending on stereo */
         pkt->duration = (chunk_size * 2) / st->codecpar->channels;
     }