Add empty pointcloud check to melodic-devel for 2.18

cpr-02-1.7.0

CORE-17208 Crash realsense passthough malloc

cpr-02-1.6.2: Merge pull request #3 from amavrinac-cpr/vgf_skip_empty_input_2

Copy input cloud into output on empty input (to retain header data).

cpr-01-1.6.2

Merge pull request #2 from amavrinac-cpr/vgf_skip_empty_input

Skip processing empty input point clouds in voxel grid filter.