avformat/iamf_parse: ensure the stream count in a scalable channel representation is equal to the audio element's stream count

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/iamf_parse.c

@@ -480,6 +480,9 @@ static int scalable_channel_layout_config(void *s, AVIOContext *pb,
             av_channel_layout_copy(&layer->ch_layout, &ch_layout);
     }
 
+    if (k != audio_element->nb_substreams)
+        return AVERROR_INVALIDDATA;
+
     return 0;
 }