fix RVIZ error for lanelet_map_rviz topic when there is no crosswalk lanelet

bug

Fixed bug

This MR removes unintended error given from RVIZ when there is no road lanelet or crosswalk lanelet in a Lanelet2 map.

Required information:

• Operating system and version:
  • Ubuntu 16.04
• Autoware installation type:
  • From source
• Autoware version or commit hash
  • master branch (2019/11/18)
• ROS distribution and version:
  • ROS Kinetic
• ROS installation type:
  • From binary
• Package or library, if applicable:
  • lanelet2_extension, map_file

Description of the bug

Rviz gives error when there is no crosswalks in a map. This is because visualization marker is published with no points.

Steps to reproduce the bug

1. Download lanelet2_tf.launchno_crosswalk.osm
2. Start runtime_manager
3. Load downloaded map and tf.launch from Map Tab.
4. Start rviz.

Expected behavior

Map loads without any error.

Actual behavior

Rviz shows following error:

TriMesh marker [crosswalk_lanelets/0] has no points.

Fix applied

This MR avoid to add empty marker for visualization.