avcodec/wmaprodec: check number of channels for XMA streams

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavcodec/wmaprodec.c

@@ -1825,8 +1825,13 @@ static av_cold int xma_decode_init(AVCodecContext *avctx)
     XMADecodeCtx *s = avctx->priv_data;
     int i, ret;
 
-    for (i = 0; i < avctx->channels / 2; i++) {
+    if (avctx->channels <= 0 || avctx->channels > 8)
+        return AVERROR_INVALIDDATA;
+
+    for (i = 0; i < (avctx->channels + 1) / 2; i++) {
         ret = decode_init(&s->xma[i], avctx);
+        if (ret < 0)
+            return ret;
         s->frames[i] = av_frame_alloc();
         if (!s->frames[i])
             return AVERROR(ENOMEM);