Fix MeshShape::clear() for safer mesh removal

[scmwang]

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

[sjahr]

Thanks!

[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 44.08%. Comparing base (abb440d) to head (55d41c2).

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             @@
##             main    #3164      +/-   ##
==========================================
- Coverage   44.44%   44.08%   -0.35%     
==========================================
  Files         698      698              
  Lines       61558    61541      -17     
  Branches     7459     7459              
==========================================
- Hits        27353    27124     -229     
- Misses      34037    34248     +211     
- Partials      168      169       +1     

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