avpacket: Fixing side data copy when src == dst

Fixing av_packet_copy_side_data to work correctly when source and
destination are the same. This makes sure that there is no memory
leak and double frees.

Signed-off by: Vignesh Venkatasubramanian <vigneshv@google.com>

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/avpacket.c

@@ -225,8 +225,10 @@ int av_copy_packet_side_data(AVPacket *pkt, AVPacket *src)
         int i;
         DUP_DATA(pkt->side_data, src->side_data,
                 src->side_data_elems * sizeof(*src->side_data), 0, ALLOC_MALLOC);
-        memset(pkt->side_data, 0,
-                src->side_data_elems * sizeof(*src->side_data));
+        if (src != pkt) {
+            memset(pkt->side_data, 0,
+                   src->side_data_elems * sizeof(*src->side_data));
+        }
         for (i = 0; i < src->side_data_elems; i++) {
             DUP_DATA(pkt->side_data[i].data, src->side_data[i].data,
                     src->side_data[i].size, 1, ALLOC_MALLOC);