GRF: Only use extended bytes for object IDs if feature is tested for

src/newgrf.cpp

@@ -6529,7 +6529,7 @@ static void ObjectMapSpriteGroup(ByteReader *buf, uint8 idcount)
 
 	uint16 *objects = AllocaM(uint16, idcount);
 	for (uint i = 0; i < idcount; i++) {
-		objects[i] = buf->ReadExtendedByte();
+		objects[i] = HasBit(_cur.grffile->observed_feature_tests, GFTOF_MORE_OBJECTS_PER_GRF) ? buf->ReadExtendedByte() : buf->ReadByte();
 	}
 
 	uint8 cidcount = buf->ReadByte();

src/newgrf_extension.cpp

@@ -57,7 +57,7 @@ extern const GRFFeatureInfo _grf_feature_list[] = {
 	GRFFeatureInfo("action0_object_viewport_map_tile_type", 1),
 	GRFFeatureInfo("road_stops", 7),
 	GRFFeatureInfo("new_landscape", 2),
-	GRFFeatureInfo("more_objects_per_grf", 1),
+	GRFFeatureInfo("more_objects_per_grf", 1, GFTOF_MORE_OBJECTS_PER_GRF),
 	GRFFeatureInfo(),
 };
 

src/newgrf_extension.h

@@ -86,6 +86,8 @@ enum Action2VariableRemapIds {
 };
 
 enum GRFFeatureTestObservationFlag : uint8 {
+	GFTOF_MORE_OBJECTS_PER_GRF = 0,
+
 	GFTOF_INVALID = 0xFF,
 };