h264: set Picture.owner2 to the current thread

This does not seem to have an effect currently. Fate-h264 passes with
THREADS=1..16 and both threading types as before. It fixes however a
segfault during error resilience with my adaptive-frame-mt patchset.
A picture in use during error resilience gets realloced in another
thread in the fuzzed sample sample_varPAR.avi_s226019.

libavcodec/h264.c

@@ -2876,10 +2876,12 @@ static int decode_slice_header(H264Context *h, H264Context *h0)
 
     if (h->slice_type_nos != AV_PICTURE_TYPE_I) {
         s->last_picture_ptr = &h->ref_list[0][0];
+        s->last_picture_ptr->owner2 = s;
         ff_copy_picture(&s->last_picture, s->last_picture_ptr);
     }
     if (h->slice_type_nos == AV_PICTURE_TYPE_B) {
         s->next_picture_ptr = &h->ref_list[1][0];
+        s->next_picture_ptr->owner2 = s;
         ff_copy_picture(&s->next_picture, s->next_picture_ptr);
     }
 

libavcodec/mpegvideo.c

@@ -1459,8 +1459,7 @@ int ff_MPV_frame_start(MpegEncContext *s, AVCodecContext *avctx)
     if (s->next_picture_ptr)
         ff_copy_picture(&s->next_picture, s->next_picture_ptr);
 
-    if (HAVE_THREADS && (avctx->active_thread_type & FF_THREAD_FRAME) &&
-        (s->out_format != FMT_H264 || s->codec_id == AV_CODEC_ID_SVQ3)) {
+    if (HAVE_THREADS && (avctx->active_thread_type & FF_THREAD_FRAME)) {
         if (s->next_picture_ptr)
             s->next_picture_ptr->owner2 = s;
         if (s->last_picture_ptr)