Fix typo bug in MaterialIndex

[azeey]

🦟 Bug fix

Summary

A typo in the following snippet was causing materialIndex to be accessed when did not contain a value.

if (this-dataPtr->materialIndex.has_value()) //  Note the `-` instead of `->` in `this-dataPtr`.
    return this->dataPtr->materialIndex.value();

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

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #338 (e955fec) into main (2a26202) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #338      +/-   ##
==========================================
+ Coverage   77.10%   77.14%   +0.03%     
==========================================
  Files          76       76              
  Lines       10548    10547       -1     
==========================================
+ Hits         8133     8136       +3     
+ Misses       2415     2411       -4     

Impacted Files	Coverage Δ
graphics/src/SubMesh.cc	91.08% <100.00%> (+1.24%)	⬆️

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[chapulina]

Ouch!