Fix loading grayscale albedo map

[iche033]

🦟 Bug fix

Fixes #464

Summary

The Urban Station model appears red when loaded in ign-gazebo. This was due to using a grayscale texture map. The single channel texture is loaded into the red component of the diffuse texture. A check for grayscale textures was added to fix this issue before but it was added inside another check that never gets reached if the material is set through the dae file (and not set through the SDF element).

This PR makes minor tweak so that all textures set to the mesh are checked to see if it's grayscale.

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

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[codecov]

Codecov Report

Merging #466 (6fffe05) into ign-rendering6 (cde3e08) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           ign-rendering6     #466   +/-   ##
===============================================
  Coverage           53.49%   53.50%           
===============================================
  Files                 192      192           
  Lines               19560    19562    +2     
===============================================
+ Hits                10464    10467    +3     
+ Misses               9096     9095    -1     

Impacted Files	Coverage Δ
ogre2/src/Ogre2Material.cc	92.13% <100.00%> (+0.32%)	⬆️

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[chapulina]

Thanks!