avcodec/dpx: respect side data preference

If the time code side data is overridden by the packet level, we also
make sure not to update `p->metadata` to a mismatched timecode.

libavcodec/dpx.c

@@ -287,12 +287,13 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *p,
         tc = av_bswap32(read32(&buf, endian));
 
         if (i != 0xFFFFFFFF) {
-            AVFrameSideData *tcside =
-                av_frame_new_side_data(p, AV_FRAME_DATA_S12M_TIMECODE,
-                                       sizeof(uint32_t) * 4);
-            if (!tcside)
-                return AVERROR(ENOMEM);
+            AVFrameSideData *tcside;
+            ret = ff_frame_new_side_data(avctx, p, AV_FRAME_DATA_S12M_TIMECODE,
+                                         sizeof(uint32_t) * 4, &tcside);
+            if (ret < 0)
+                return ret;
 
+            if (tcside) {
                 tc_sd = (uint32_t*)tcside->data;
                 tc_sd[0] = 1;
                 tc_sd[1] = tc;
@@ -302,6 +303,7 @@ static int decode_frame(AVCodecContext *avctx, AVFrame *p,
                 av_dict_set(&p->metadata, "timecode", tcbuf, 0);
             }
         }
+    }
 
     /* color range from television header */
     if (offset >= 1964 + 4) {