Fix joint controller with empty joint velocity data

[iche033]

Signed-off-by: Ian Chen ichen@osrfoundation.org

🦟 Bug fix

Summary

Joint controller system assumes that joint velocity data is always available and tries to access the data by indexing into an std::vector object. However, if the physics system is not loaded, the vector will be empty and the system will throw an 'std::out_of_range' error. This PR checks for empty vector before doing any indexing.

One example of this happening is when trying to run the collada exporter of a model that has a joint controller but in a world without the physics system.

To reproduce:

Here's the world file

tmp_world.sdf

<sdf version="1.6">
  <world name="marble_hd2_sensor_config_1">
    <plugin 
      filename="ignition-gazebo-collada-world-exporter-system" 
      name="ignition::gazebo::systems::ColladaWorldExporter">
    </plugin>
    <include>
      <static>true</static>
      <name>body</name>
      <pose>0 0 0 0 0 0</pose>
      <uri>https://fuel.ignitionrobotics.org/1.0/OpenRobotics/models/marble_hd2_sensor_config_1</uri>
    </include>
  </world> 
</sdf>

and run this cmd:

ign gazebo -s -r --iterations 1 tmp_world.sdf

Without the changes in this PR, you should get a crash with backtrace pointing to the joint controller system

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

Merging #937 (385d542) into ign-gazebo4 (488cc87) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

❗ Current head 385d542 differs from pull request most recent head f2d8825. Consider uploading reports for the commit f2d8825 to get more accurate results

@@               Coverage Diff               @@
##           ign-gazebo4     #937      +/-   ##
===============================================
- Coverage        65.98%   65.92%   -0.06%     
===============================================
  Files              239      239              
  Lines            17686    17688       +2     
===============================================
- Hits             11670    11661       -9     
- Misses            6016     6027      +11     

Impacted Files	Coverage Δ
src/systems/joint_controller/JointController.cc	77.65% <100.00%> (+0.48%)	⬆️
...int_position_controller/JointPositionController.cc	53.14% <0.00%> (-7.43%)	⬇️
src/gui/GuiRunner.cc	88.00% <0.00%> (+2.66%)	⬆️

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