Visual cloning: check for null children and recursively delete cloned visuals if failure occurs

[adlarkin]

Signed-off-by: Ashton Larkin ashton@openrobotics.org

🦟 Bug fix

Summary

Follow-up to #397

If cloning a visual fails, we should destroy the top-level cloned visual recursively in order to ensure that all cloned child visuals are also destroyed. I also added a check to make sure that the child visual to clone isn't nullptr.

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 #434 (2944bc9) into main (45a49f0) will decrease coverage by 0.01%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##             main     #434      +/-   ##
==========================================
- Coverage   55.12%   55.11%   -0.02%     
==========================================
  Files         192      192              
  Lines       19381    19383       +2     
==========================================
- Hits        10683    10682       -1     
- Misses       8698     8701       +3     

Impacted Files	Coverage Δ
include/ignition/rendering/base/BaseVisual.hh	70.20% <25.00%> (-1.23%)	⬇️

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