collision_distance_field: Fix undefined behavior vector insertion

[JafarAbdi]

Description

Backport of moveit/moveit2#942

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[codecov]

Codecov Report

Merging #3017 (27d2c41) into master (155eefa) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3017      +/-   ##
==========================================
- Coverage   61.80%   61.79%   -0.00%     
==========================================
  Files         371      371              
  Lines       33167    33167              
==========================================
- Hits        20494    20493       -1     
- Misses      12673    12674       +1     

Impacted Files	Coverage Δ
...istance_field/src/collision_env_distance_field.cpp	63.71% <0.00%> (ø)
...eit_ros/manipulation/pick_place/src/pick_place.cpp	88.58% <0.00%> (-3.80%)	⬇️
...ipulation/pick_place/src/manipulation_pipeline.cpp	71.91% <0.00%> (-2.47%)	⬇️
moveit_core/robot_state/src/robot_state.cpp	52.36% <0.00%> (+0.08%)	⬆️
..._interface/src/detail/constrained_goal_sampler.cpp	76.48% <0.00%> (+1.97%)	⬆️
...meterization/work_space/pose_model_state_space.cpp	81.77% <0.00%> (+2.36%)	⬆️

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[rhaschke]

Indeed, PosedBodyPointDecompositionVector::getCollisionPoints() returns an new object on each call:
https://github.com/ros-planning/moveit/blob/ef085558818e7e4fbc97e41f8dd12a1a2d6dbfa0/moveit_core/collision_distance_field/include/moveit/collision_distance_field/collision_distance_field_types.h#L445-L453