avpacket: Initialize the allocated padding area in side data

This makes sure that consumers of the side data actually can
rely on the padding as intended, without having the callers of
av_packet_new_side_data to explicitly zero initialize it.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/avpacket.c

@@ -271,6 +271,7 @@ uint8_t *av_packet_new_side_data(AVPacket *pkt, enum AVPacketSideDataType type,
     data = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
     if (!data)
         return NULL;
+    memset(data + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
 
     ret = av_packet_add_side_data(pkt, type, data, size);
     if (ret < 0) {