message: safe access in GenerateRoadCorridorLane
diff: @@ -211,9 +211,13 @@ void MapInterface::CalculateLaneCorridors(
  LanePtr MapInterface::GenerateRoadCorridorLane(const XodrLanePtr& xodr_lane) {
  LanePtr lane = std::make_shared<Lane>(xodr_lane);
  // polygons
  + if (xodr_lane->get_lane_position() != 0) {
  std::pair<PolygonPtr, bool> polygon_success =
  roadgraph_->ComputeXodrLanePolygon(xodr_lane->get_id());
  + // Cannot compute polygon for planview!!
  + if (polygon_success.second)
  lane->SetPolygon(*polygon_success.first);
  + }
  return lane;
  }
  