Fix: NewGRF house class mappings were not reset between games. (#11279)

(cherry picked from commit 6643c010bd)

src/newgrf_house.cpp

@@ -29,7 +29,7 @@
 #include "table/strings.h"
 
 static BuildingCounts<uint32> _building_counts;
-static HouseClassMapping _class_mapping[HOUSE_CLASS_MAX];
+static std::array<HouseClassMapping, HOUSE_CLASS_MAX> _class_mapping;
 
 HouseOverrideManager _house_mngr(NEW_HOUSE_OFFSET, NUM_HOUSES, INVALID_HOUSE_ID);
 
@@ -105,6 +105,11 @@ uint32 FakeHouseResolverObject::GetDebugID() const
 	return HouseSpec::Get(this->house_scope.house_id)->grf_prop.local_id;
 }
 
+void ResetHouseClassIDs()
+{
+	_class_mapping = {};
+}
+
 HouseClassID AllocateHouseClassID(byte grf_class_id, uint32 grfid)
 {
 	/* Start from 1 because 0 means that no class has been assigned. */

src/newgrf_house.h

@@ -134,6 +134,7 @@ struct HouseClassMapping {
 	uint8  class_id;  ///< The class id within the grf file
 };
 
+void ResetHouseClassIDs();
 HouseClassID AllocateHouseClassID(byte grf_class_id, uint32 grfid);
 
 void InitializeBuildingCounts();

src/town_cmd.cpp

@@ -4452,6 +4452,8 @@ HouseSpec _house_specs[NUM_HOUSES];
 
 void ResetHouses()
 {
+	ResetHouseClassIDs();
+
 	auto insert = std::copy(std::begin(_original_house_specs), std::end(_original_house_specs), std::begin(_house_specs));
 	std::fill(insert, std::end(_house_specs), HouseSpec{});