Handle case where rail waypoint runs out of station spec slots

src/waypoint_cmd.cpp

@@ -280,6 +280,10 @@ CommandCost CmdBuildRailWaypoint(TileIndex start_tile, DoCommandFlag flags, uint
 		if (!Waypoint::CanAllocateItem()) return_cmd_error(STR_ERROR_TOO_MANY_STATIONS_LOADING);
 	}
 
+	/* Check if we can allocate a custom stationspec to this station */
+	int map_spec_index = AllocateSpecToStation(spec, wp, (flags & DC_EXEC) != 0);
+	if (map_spec_index == -1) return_cmd_error(STR_ERROR_TOO_MANY_STATION_SPECS);
+
 	if (flags & DC_EXEC) {
 		if (wp == nullptr) {
 			wp = new Waypoint(start_tile);
@@ -301,8 +305,6 @@ CommandCost CmdBuildRailWaypoint(TileIndex start_tile, DoCommandFlag flags, uint
 
 		wp->UpdateVirtCoord();
 
-		byte map_spec_index = AllocateSpecToStation(spec, wp, true);
-
 		Company *c = Company::Get(wp->owner);
 		for (int i = 0; i < count; i++) {
 			TileIndex tile = start_tile + i * offset;