mxfdec: skip to end of structural sets

This fixes reading of partition packs. The code stops reading after the
operational pattern and should skip the array of essence container
labels that follow.
Signed-off-by: Janne Grunau <janne-libav@jannau.net>

libavformat/mxfdec.c

@@ -1053,8 +1053,11 @@ static int mxf_read_header(AVFormatContext *s, AVFormatParameters *ap)
                 int res;
                 if (klv.key[5] == 0x53) {
                     res = mxf_read_local_tags(mxf, &klv, metadata->read, metadata->ctx_size, metadata->type);
-                } else
+                } else {
+                    uint64_t next = avio_tell(s->pb) + klv.length;
                     res = metadata->read(mxf, s->pb, 0, 0, klv.key);
+                    avio_seek(s->pb, next, SEEK_SET);
+                }
                 if (res < 0) {
                     av_log(s, AV_LOG_ERROR, "error reading header metadata\n");
                     return res;