[jog_arm] Fix crash on empty jog msgs

[rfeistenauer]

Description

Added a Point message to an empty joint_trajectory to prevent the jog server to crash on icall of invalid index.

• fixes jog_server dies if first msg is a joint_delta_jog_cmd #2047

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

[welcome]

Thanks for helping in improving MoveIt and open source robotics!

[codecov-commenter]

Codecov Report

Merging #2094 into master will increase coverage by 3.72%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #2094      +/-   ##
==========================================
+ Coverage   54.07%   57.80%   +3.72%     
==========================================
  Files         319      328       +9     
  Lines       25019    25663     +644     
==========================================
+ Hits        13530    14834    +1304     
+ Misses      11489    10829     -660     

Impacted Files	Coverage Δ
...veit_experimental/moveit_jog_arm/src/jog_calcs.cpp	72.97% <66.66%> (-2.03%)	⬇️
.../ompl_interface/src/detail/constrained_sampler.cpp	46.15% <0.00%> (-17.95%)	⬇️
...rimental/moveit_jog_arm/src/jog_interface_base.cpp	73.01% <0.00%> (-5.62%)	⬇️
...cessing/src/time_optimal_trajectory_generation.cpp	75.83% <0.00%> (-0.37%)	⬇️
...raint_samplers/src/default_constraint_samplers.cpp	82.54% <0.00%> (-0.37%)	⬇️
...pl/ompl_interface/src/planning_context_manager.cpp	70.94% <0.00%> (-0.17%)	⬇️
...veit_core/robot_model/src/floating_joint_model.cpp	48.35% <0.00%> (ø)
...bot_state/include/moveit/robot_state/robot_state.h	91.02% <0.00%> (ø)
...veit_jog_arm/include/moveit_jog_arm/jog_arm_data.h	100.00% <0.00%> (ø)
... and 52 more

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[AndyZe]

Just noticed that the tutorial was crashing because of this issue. Great catch!

To be consistent, can you please delete L81 of jog_calcs.cpp? Because the "effort" field isn't used. Delete this line:

internal_joint_state_.effort.resize(num_joints_);

[v4hn]

I removed the line as requested by @AndyZe .

I take it this can be merged once CI passes.

[rfeistenauer]

Thanks both @AndyZe for the review and @v4hn for adding the requested change.
I gues this can be merged now.

[AndyZe]

Thanks v4hn. Looks ready to merge to me, too

[tylerjw]

lgtm... I tested this and it fixes the bug. Please merge as we need this to have a stable melodic backport of jog_arm.

[welcome]

Congrats on getting your first MoveIt pull request merged and improving open source robotics!