asfdec: fix assert failure on invalid files

Add an extra size validity check in asf_read_frame_header(). Without
this asf->packet_size_left may become negative, which triggers an
assertion failure later.

libavformat/asfdec.c

@@ -842,6 +842,10 @@ static int asf_read_frame_header(AVFormatContext *s, AVIOContext *pb){
         av_log(s, AV_LOG_ERROR, "unexpected packet_replic_size of %d\n", asf->packet_replic_size);
         return -1;
     }
+    if (rsize > asf->packet_size_left) {
+        av_log(s, AV_LOG_ERROR, "packet_replic_size is invalid\n");
+        return -1;
+    }
     if (asf->packet_flags & 0x01) {
         DO_2BITS(asf->packet_segsizetype >> 6, asf->packet_frag_size, 0); // 0 is illegal
         if(asf->packet_frag_size > asf->packet_size_left - rsize){