Fix tunnels underground view merge issue with custom bridgeheads.

src/roadveh_cmd.cpp

@@ -1181,7 +1181,7 @@ bool IndividualRoadVehicleController(RoadVehicle *v, const RoadVehicle *prev)
 			v->x_pos = gp.x;
 			v->y_pos = gp.y;
 			v->UpdatePosition();
-			if ((v->vehstatus & VS_HIDDEN) == 0) v->Vehicle::UpdateViewport(true);
+			if (v->IsDrawn()) v->Vehicle::UpdateViewport(true);
 			return true;
 		}
 	}