use internal video frame number

Originally committed as revision 13479 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/swfenc.c

@@ -494,7 +494,7 @@ static int swf_write_trailer(AVFormatContext *s)
         url_fseek(pb, 4, SEEK_SET);
         put_le32(pb, file_size);
         url_fseek(pb, swf->duration_pos, SEEK_SET);
-        put_le16(pb, video_enc->frame_number);
+        put_le16(pb, swf->video_frame_number);
         url_fseek(pb, file_size, SEEK_SET);
     }
     return 0;