avcodec/wavpackenc: Check the number of channels

They are stored in a byte, thus more than 255 is not possible
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/wavpackenc.c

@@ -128,6 +128,11 @@ static av_cold int wavpack_encode_init(AVCodecContext *avctx)
 
     s->avctx = avctx;
 
+    if (avctx->channels > 255) {
+        av_log(avctx, AV_LOG_ERROR, "Too many channels\n", avctx->channels);
+        return AVERROR(EINVAL);
+    }
+
     if (!avctx->frame_size) {
         int block_samples;
         if (!(avctx->sample_rate & 1))