interplayacm: validate number of channels

The number of channels is used as divisor in decode_frame, so it must
not be zero to avoid SIGFPE crashes.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavcodec/interplayacm.c

@@ -62,6 +62,11 @@ static av_cold int decode_init(AVCodecContext *avctx)
     if (avctx->extradata_size < 14)
         return AVERROR_INVALIDDATA;
 
+    if (avctx->channels <= 0) {
+        av_log(avctx, AV_LOG_ERROR, "Invalid number of channels: %d\n", avctx->channels);
+        return AVERROR_INVALIDDATA;
+    }
+
     s->level = AV_RL16(avctx->extradata + 12) & 0xf;
     s->rows  = AV_RL16(avctx->extradata + 12) >>  4;
     s->cols  = 1 << s->level;