Output warning message if a mesh with zero submeshes is created

[iche033]

🦟 Bug fix

Summary

Currently if a ign-gazebo user specifies a non-existent submesh through the <submesh> SDF element, an empty mesh with no submeshes will be created. The newly added warning msg is useful to help catch issues / typos with incorrectly specified submesh name.

To test:

you can change a submesh name in one of the ign-gazebo example worlds to see the warning msg printed in the console, e.g. edit tunnel.sdf and change this submesh from BodyFront to FrontBody then launch the tunnel world.

ign gazebo -v 4 tunnel.sdf

and you should see this warning msg:

[GUI] [Wrn] [Ogre2MeshFactory.cc:478] Unable to load mesh: 'https://fuel.ignitionrobotics.org/1.0/OpenRobotics/models/EXPLORER_R2_SENSOR_CONFIG_2/3/files/meshes/r2.dae', submesh: 'FrontBody'. Mesh will be empty.

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)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

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[codecov]

Codecov Report

Merging #391 (b588a4f) into ign-rendering4 (f65f2fa) will decrease coverage by 0.04%.
The diff coverage is 8.33%.

@@                Coverage Diff                 @@
##           ign-rendering4     #391      +/-   ##
==================================================
- Coverage           55.93%   55.89%   -0.05%     
==================================================
  Files                 147      147              
  Lines               13964    13976      +12     
==================================================
+ Hits                 7811     7812       +1     
- Misses               6153     6164      +11     

Impacted Files	Coverage Δ
ogre/src/OgreMeshFactory.cc	1.08% <0.00%> (-0.03%)	⬇️
ogre2/src/Ogre2MeshFactory.cc	81.88% <16.66%> (-1.45%)	⬇️

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