avformat/utils: ensure that all packets in AVPacketList are reference counted

This is done so that its data is really owned by the packet.
This was already true for the current callers.
Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/internal.h

@@ -763,7 +763,8 @@ void ff_format_set_url(AVFormatContext *s, char *url);
  *
  * @param head  List head element
  * @param tail  List tail element
- * @param pkt   The packet being appended
+ * @param pkt   The packet being appended. The data described in it will
+ *              be made reference counted if it isn't already.
  * @param flags Any combination of FF_PACKETLIST_FLAG_* flags
  * @return 0 on success, negative AVERROR value on failure. On failure,
            the list is unchanged

libavformat/utils.c

@@ -460,6 +460,11 @@ int ff_packet_list_put(AVPacketList **packet_buffer,
             return ret;
         }
     } else {
+        ret = av_packet_make_refcounted(pkt);
+        if (ret < 0) {
+            av_free(pktl);
+            return ret;
+        }
         av_packet_move_ref(&pktl->pkt, pkt);
     }