Fix crash when clearing tunnel where only near end is reserved with realistic braking

src/tunnelbridge_cmd.cpp

@@ -1206,13 +1206,17 @@ static CommandCost DoClearTunnel(TileIndex tile, DoCommandFlag flags)
 		if (ret.Failed()) return ret;
 	}
 
-	if (GetTunnelBridgeTransportType(tile) == TRANSPORT_RAIL && _settings_game.vehicle.train_braking_model == TBM_REALISTIC && HasTunnelReservation(tile)) {
+	if (GetTunnelBridgeTransportType(tile) == TRANSPORT_RAIL && _settings_game.vehicle.train_braking_model == TBM_REALISTIC) {
 		DiagDirection dir = GetTunnelBridgeDirection(tile);
 		Track track = DiagDirToDiagTrack(dir);
-		CommandCost ret = CheckTrainReservationPreventsTrackModification(tile, track);
-		if (ret.Failed()) return ret;
-		ret = CheckTrainReservationPreventsTrackModification(endtile, track);
-		if (ret.Failed()) return ret;
+		if (HasTunnelReservation(tile)) {
+			CommandCost ret = CheckTrainReservationPreventsTrackModification(tile, track);
+			if (ret.Failed()) return ret;
+		}
+		if (HasTunnelReservation(endtile)) {
+			ret = CheckTrainReservationPreventsTrackModification(endtile, track);
+			if (ret.Failed()) return ret;
+		}
 	}
 
 	/* checks if the owner is town then decrease town rating by RATING_TUNNEL_BRIDGE_DOWN_STEP until