fix config not saving

gframe/game.cpp

@@ -1459,6 +1459,7 @@ void Game::SaveConfig() {
 	char linebuf[CONFIG_LINE_SIZE];
 	std::fprintf(fp, "use_d3d = %d\n", gameConf.use_d3d ? 1 : 0);
 	std::fprintf(fp, "use_image_scale = %d\n", gameConf.use_image_scale ? 1 : 0);
+	std::fprintf(fp, "use_image_load_background_thread = %d\n", gameConf.use_image_load_background_thread ? 1 : 0);
 	std::fprintf(fp, "antialias = %d\n", gameConf.antialias);
 	std::fprintf(fp, "errorlog = %u\n", enable_log);
 	BufferIO::CopyWideString(ebNickName->getText(), gameConf.nickname);