h264: add missing brackets.

This caused failure of a few fate tests.

libavcodec/h264_refs.c

@@ -515,9 +515,10 @@ int ff_h264_execute_ref_pic_marking(H264Context *h, MMCO *mmco, int mmco_count){
             pic = find_short(h, frame_num, &j);
             if(!pic){
                 if(mmco[i].opcode != MMCO_SHORT2LONG || !h->long_ref[mmco[i].long_arg]
-                   || h->long_ref[mmco[i].long_arg]->frame_num != frame_num)
-                av_log(h->s.avctx, AV_LOG_ERROR, "mmco: unref short failure\n");
-                err = AVERROR_INVALIDDATA;
+                   || h->long_ref[mmco[i].long_arg]->frame_num != frame_num) {
+                    av_log(h->s.avctx, AV_LOG_ERROR, "mmco: unref short failure\n");
+                    err = AVERROR_INVALIDDATA;
+                }
                 continue;
             }
         }