avformat/movenc: Avoid loosing cluster array on failure

Fixes: crash
Fixes: check_pkt.mp4

Found-by: Rafael Dutra <rafael.dutra@cispa.de>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 5c2ff44f91)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/movenc.c

@@ -5746,11 +5746,12 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
 
     if (trk->entry >= trk->cluster_capacity) {
         unsigned new_capacity = trk->entry + MOV_INDEX_CLUSTER_SIZE;
-        if (av_reallocp_array(&trk->cluster, new_capacity,
-                              sizeof(*trk->cluster))) {
+        void *cluster = av_realloc_array(trk->cluster, new_capacity, sizeof(*trk->cluster));
+        if (!cluster) {
             ret = AVERROR(ENOMEM);
             goto err;
         }
+        trk->cluster          = cluster;
         trk->cluster_capacity = new_capacity;
     }