pthread_frame: don't sync items between threads for intra-only codecs.

Intra-only codecs should either be able to read these items from the
bitstream, or they should be set upon codec initialization. In both
cases, syncing these items at runtime is unnecessary.

In practice, this fixes race conditions for decoders that read these
values from the bitstream.

libavcodec/pthread_frame.c

@@ -244,7 +244,7 @@ static int update_context_from_thread(AVCodecContext *dst, AVCodecContext *src,
 {
     int err = 0;
 
-    if (dst != src) {
+    if (dst != src && (for_user || !(av_codec_get_codec_descriptor(src)->props & AV_CODEC_PROP_INTRA_ONLY))) {
         dst->time_base = src->time_base;
         dst->framerate = src->framerate;
         dst->width     = src->width;