avcodec/wrapped_avframe: Don't presume AVPacket to be writable

It need not be writable; in fact, it is often not writable even if
the packet sent to the decoder was writable, because the generic code
calls av_packet_ref() on it. It is never writable if a user
drains the decoder after every packet, because in this case the decode
callback is called from avcodec_send_packet().

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/wrapped_avframe.c

@@ -92,7 +92,9 @@ static int wrapped_avframe_decode(AVCodecContext *avctx, AVFrame *out,
 
     in  = (AVFrame*)pkt->data;
 
-    av_frame_move_ref(out, in);
+    err = av_frame_ref(out, in);
+    if (err < 0)
+        return err;
 
     err = ff_decode_frame_props(avctx, out);
     if (err < 0)