avcodec/amfnec: allocate packets using av_new_packet()

This ensures they will be reference counted, as required by the AVCodec.receive_packet()
API.

Should fix ticket #8386.

Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit fdf46b4a6b)

libavcodec/amfenc.c

@@ -438,7 +438,7 @@ static int amf_copy_buffer(AVCodecContext *avctx, AVPacket *pkt, AMFBuffer *buff
     int64_t          timestamp = AV_NOPTS_VALUE;
     int64_t          size = buffer->pVtbl->GetSize(buffer);
 
-    if ((ret = ff_alloc_packet2(avctx, pkt, size, 0)) < 0) {
+    if ((ret = av_new_packet(pkt, size)) < 0) {
         return ret;
     }
     memcpy(pkt->data, buffer->pVtbl->GetNative(buffer), size);