avcodec/cook: check that the subpacket sizes fit in block_align

Fixes out of array read
Fixes: asan_heap-oob_fb5c50_19_018.rmvb
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/cook.c

@@ -1215,8 +1215,8 @@ static av_cold int cook_decode_init(AVCodecContext *avctx)
 
         q->num_subpackets++;
         s++;
-        if (s > MAX_SUBPACKETS) {
-            avpriv_request_sample(avctx, "subpackets > %d", MAX_SUBPACKETS);
+        if (s > FFMIN(MAX_SUBPACKETS, avctx->block_align)) {
+            avpriv_request_sample(avctx, "subpackets > %d", FFMIN(MAX_SUBPACKETS, avctx->block_align));
             return AVERROR_PATCHWELCOME;
         }
     }