Fix 85a49a0d: invalidate airport toolbar when new planes become available (#8532)

Otherwise if the airport button is disabled, it will remain disabled
until you close/open the toolbar again.

src/engine.cpp

@@ -735,6 +735,7 @@ static void EnableEngineForCompany(EngineID eid, CompanyID company)
 		InvalidateWindowData(WC_MAIN_TOOLBAR, 0);
 		if (e->type == VEH_ROAD) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_ROAD);
 		if (e->type == VEH_SHIP) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_WATER);
+		if (e->type == VEH_AIRCRAFT) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_AIR);
 	}
 }
 
@@ -1018,6 +1019,7 @@ static void NewVehicleAvailable(Engine *e)
 	/* Update the toolbar. */
 	if (e->type == VEH_ROAD) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_ROAD);
 	if (e->type == VEH_SHIP) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_WATER);
+	if (e->type == VEH_AIRCRAFT) InvalidateWindowData(WC_BUILD_TOOLBAR, TRANSPORT_AIR);
 
 	/* Close pending preview windows */
 	DeleteWindowById(WC_ENGINE_PREVIEW, index);