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

---

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

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

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

Project coverage is 51.26%. Comparing base (d13d835) to head (aabdb18).
Report is 1 commits behind head on humble.

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

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           humble    #3166      +/-   ##
==========================================
+ Coverage   42.26%   51.26%   +9.00%     
==========================================
  Files         668      382     -286     
  Lines       57740    31885   -25855     
  Branches     7322        0    -7322     
==========================================
- Hits        24398    16342    -8056     
+ Misses      33157    15543   -17614     
+ Partials      185        0     -185     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.