avformat/swfdec: Use side data to communicate w/h changes to the decoder

Fixes reading from freed data
Fixes part of Ticket3539
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/swfdec.c

@@ -353,11 +353,15 @@ static int swf_read_packet(AVFormatContext *s, AVPacket *pkt)
                 avpriv_set_pts_info(vst, 64, 256, swf->frame_rate);
                 st = vst;
             }
-            st->codec->width  = width;
-            st->codec->height = height;
 
             if ((res = av_new_packet(pkt, out_len - colormapsize * colormapbpp)) < 0)
                 goto bitmap_end;
+            if (!st->codec->width && !st->codec->height) {
+                st->codec->width  = width;
+                st->codec->height = height;
+            } else {
+                ff_add_param_change(pkt, 0, 0, 0, width, height);
+            }
             pkt->pos = pos;
             pkt->stream_index = st->index;