rtmppkt: Make pkt->data reallocable

We try to avoid mixing av_malloc with av_realloc, since av_malloc
may be implemented with functions that can't (formally) be mixed
with the functions used in av_realloc.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtmppkt.c

@@ -395,7 +395,7 @@ int ff_rtmp_packet_create(RTMPPacket *pkt, int channel_id, RTMPPacketType type,
                           int timestamp, int size)
 {
     if (size) {
-        pkt->data = av_malloc(size);
+        pkt->data = av_realloc(NULL, size);
         if (!pkt->data)
             return AVERROR(ENOMEM);
     }