NewGRF: Only extend value of road stops variable 68 if feature tested for

src/newgrf_extension.h

@@ -79,6 +79,7 @@ enum Action2VariableRemapIds {
 	A2VRI_OBJECT_FOUNDATION_SLOPE = 0x100,
 	A2VRI_OBJECT_FOUNDATION_SLOPE_CHANGE,
 	A2VRI_VEHICLE_CURRENT_SPEED_SCALED,
+	A2VRI_ROADSTOP_INFO_NEARBY_TILES_EXT,
 	A2VRI_ROADSTOP_INFO_NEARBY_TILES_V2,
 	A2VRI_RAILTYPE_SIGNAL_RESTRICTION_INFO,
 	A2VRI_RAILTYPE_SIGNAL_CONTEXT,
@@ -105,6 +106,7 @@ enum GRFFeatureTestObservationFlag : uint8 {
 	GFTOF_TOWN_ZONE_CALLBACK,
 	GFTOF_MORE_VARACTION2_TYPES,
 	GFTOF_MULTI_PART_SHIPS,
+	GFTOF_ROAD_STOPS,
 
 	GFTOF_INVALID = 0xFF,
 };