Move GRF global var init to common function

src/openttd.cpp

@@ -485,10 +485,9 @@ static void ShutdownGame()
 	_game_load_date_fract = 0;
 	_game_load_tick_skip_counter = 0;
 	_game_load_time = 0;
-	_extra_station_names_used = 0;
-	_extra_station_names_probability = 0;
 	_extra_aspects = 0;
 	_aspect_cfg_hash = 0;
+	InitGRFGlobalVars();
 	_loadgame_DBGL_data.clear();
 	_loadgame_DBGC_data.clear();
 }