ray_ground_filter crashes on empty clouds

[Timple]

Bug report

Required information:

• Operating system and version:
  • Ubuntu 18.04
• Autoware installation type:
  • None
• Autoware version or commit hash
  • core_perception latest master
• ROS distribution and version:
  • melodic
• ROS installation type:
  • git clone
• Package or library, if applicable:
  • points_preprocessor

Description of the bug

ray_ground_filter crashes on empty clouds

Steps to reproduce the bug

Send an empty cloud to the ray_ground_filter

Expected behavior

Not crashing, just forward the cloud (no ground in an empty message).

Actual behavior

Crash

Screenshots

Additional information