Enable vehicle list buttons in station GUI when list would be non-empty

src/station_gui.cpp

@@ -1399,12 +1399,18 @@ struct StationViewWindow : public Window {
 
 		this->vscroll->SetCount(cargo.GetNumChildren()); // update scrollbar
 
+		byte have_veh_types = 0;
+		IterateOrderRefcountMapForDestinationID(st->index, [&](CompanyID cid, OrderType order_type, VehicleType veh_type, uint32 refcount) {
+			SetBit(have_veh_types, veh_type);
+			return true;
+		});
+
 		/* disable some buttons */
 		this->SetWidgetDisabledState(WID_SV_RENAME,   st->owner != _local_company);
-		this->SetWidgetDisabledState(WID_SV_TRAINS,   !(st->facilities & FACIL_TRAIN));
-		this->SetWidgetDisabledState(WID_SV_ROADVEHS, !(st->facilities & FACIL_TRUCK_STOP) && !(st->facilities & FACIL_BUS_STOP));
-		this->SetWidgetDisabledState(WID_SV_SHIPS,    !(st->facilities & FACIL_DOCK));
-		this->SetWidgetDisabledState(WID_SV_PLANES,   !(st->facilities & FACIL_AIRPORT));
+		this->SetWidgetDisabledState(WID_SV_TRAINS,   !(st->facilities & FACIL_TRAIN) && !HasBit(have_veh_types, VEH_TRAIN));
+		this->SetWidgetDisabledState(WID_SV_ROADVEHS, !(st->facilities & FACIL_TRUCK_STOP) && !(st->facilities & FACIL_BUS_STOP) && !HasBit(have_veh_types, VEH_ROAD));
+		this->SetWidgetDisabledState(WID_SV_SHIPS,    !(st->facilities & FACIL_DOCK) && !HasBit(have_veh_types, VEH_SHIP));
+		this->SetWidgetDisabledState(WID_SV_PLANES,   !(st->facilities & FACIL_AIRPORT) && !HasBit(have_veh_types, VEH_AIRCRAFT));
 		this->SetWidgetDisabledState(WID_SV_CLOSE_AIRPORT, !(st->facilities & FACIL_AIRPORT) || st->owner != _local_company || st->owner == OWNER_NONE); // Also consider SE, where _local_company == OWNER_NONE
 		this->SetWidgetLoweredState(WID_SV_CLOSE_AIRPORT, (st->facilities & FACIL_AIRPORT) && (st->airport.flags & AIRPORT_CLOSED_block) != 0);