avformat/asfdec: Allow packet_obj_size == 0

Fixes Ticket3521
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/asfdec.c

@@ -1062,7 +1062,7 @@ static int asf_read_frame_header(AVFormatContext *s, AVIOContext *pb)
         int64_t end = avio_tell(pb) + asf->packet_replic_size;
         AVRational aspect;
         asfst->packet_obj_size = avio_rl32(pb);
-        if (asfst->packet_obj_size >= (1 << 24) || asfst->packet_obj_size <= 0) {
+        if (asfst->packet_obj_size >= (1 << 24) || asfst->packet_obj_size < 0) {
             av_log(s, AV_LOG_ERROR, "packet_obj_size %d invalid\n", asfst->packet_obj_size);
             asfst->packet_obj_size = 0;
             return AVERROR_INVALIDDATA;