mux: Do not leave stale side data pointers in ff_interleave_add_packet()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavformat/mux.c

@@ -419,6 +419,8 @@ FF_DISABLE_DEPRECATION_WARNINGS
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
     pkt->buf       = NULL;
+    pkt->side_data = NULL;
+    pkt->side_data_elems = 0;
     // Duplicate the packet if it uses non-allocated memory
     if ((ret = av_dup_packet(&this_pktl->pkt)) < 0) {
         av_free(this_pktl);