Fix MeshShape::clear() for safer mesh removal (backport #3164)

[mergify]

Description

To address #3162 (comment), I add a check to retrieve the mesh by name before attempting to remove it.

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

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This is an automatic backport of pull request #3164 done by [Mergify](https://mergify.com).

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 44.06%. Comparing base (e94c891) to head (8fb3bbc).
Report is 1 commits behind head on jazzy.

Files with missing lines	Patch %	Lines
...zation/rviz_plugin_render_tools/src/mesh_shape.cpp	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##            jazzy    #3167      +/-   ##
==========================================
- Coverage   44.07%   44.06%   -0.00%     
==========================================
  Files         698      698              
  Lines       61535    61539       +4     
  Branches     7457     7458       +1     
==========================================
- Hits        27115    27113       -2     
- Misses      34252    34258       +6     
  Partials      168      168              

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