Fix segfault in PSM::clearOctomap()

[henningkayser]

I randomly ran into this, the warning message should be self-explanatory.

[codecov]

Codecov Report

Merging #2193 into master will increase coverage by 0.42%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #2193      +/-   ##
==========================================
+ Coverage   57.69%   58.11%   +0.42%     
==========================================
  Files         326      326              
  Lines       25661    24730     -931     
==========================================
- Hits        14805    14372     -433     
+ Misses      10856    10358     -498     

Impacted Files	Coverage Δ
...nning_scene_monitor/src/planning_scene_monitor.cpp	69.89% <0.00%> (-0.66%)	⬇️
...moveit/move_group_interface/move_group_interface.h	57.89% <0.00%> (-2.11%)	⬇️
...ipulation/pick_place/src/manipulation_pipeline.cpp	76.41% <0.00%> (-0.95%)	⬇️
...raint_samplers/src/default_constraint_samplers.cpp	82.54% <0.00%> (-0.37%)	⬇️
moveit_core/robot_state/src/robot_state.cpp	47.39% <0.00%> (+0.09%)	⬆️
...meterization/work_space/pose_model_state_space.cpp	82.99% <0.00%> (+0.68%)	⬆️
...on/pick_place/src/approach_and_translate_stage.cpp	73.60% <0.00%> (+0.79%)	⬆️
...anning_scene_monitor/src/current_state_monitor.cpp	52.82% <0.00%> (+1.53%)	⬆️
...dl_kinematics_plugin/src/kdl_kinematics_plugin.cpp	79.37% <0.00%> (+2.69%)	⬆️
... and 2 more

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[tylerjw]

good catch, it is good to test before using