yop: Clear all references to the AVBuffer in the local AVPacket

This makes sure that it doesn't try to free an AVBuffer belonging
to an earlier packet when we free the local packet at the end.

Reported-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/yop.c

@@ -127,6 +127,12 @@ static int yop_read_packet(AVFormatContext *s, AVPacket *pkt)
     if (yop->video_packet.data) {
         *pkt                   =  yop->video_packet;
         yop->video_packet.data =  NULL;
+        yop->video_packet.buf  =  NULL;
+#if FF_API_DESTRUCT_PACKET
+FF_DISABLE_DEPRECATION_WARNINGS
+        yop->video_packet.destruct = NULL;
+FF_ENABLE_DEPRECATION_WARNINGS
+#endif
         yop->video_packet.size =  0;
         pkt->data[0]           =  yop->odd_frame;
         pkt->flags             |= AV_PKT_FLAG_KEY;