Partial fix for emissive map

[iche033]

Signed-off-by: Ian Chen ichen@osrfoundation.org

🦟 Bug fix

Partial fix for #499

Summary

When porting to ogre 2.2, lightmap and emissive map share the same texture slot. The fix adds a check to make sure we don't accidentally clear the emissive map when clearing out the lightmap texture.

There is still an issue of using grayscale emissive maps, in ogre2.2 it's being treated as RGB and so it's rendered red. This needs to be fixed next.

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 #501 (2907375) into ign-rendering6 (ae292a8) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           ign-rendering6     #501   +/-   ##
===============================================
  Coverage           55.53%   55.53%           
===============================================
  Files                 195      195           
  Lines               19697    19698    +1     
===============================================
+ Hits                10938    10939    +1     
  Misses               8759     8759           

Impacted Files	Coverage Δ
ogre2/src/Ogre2Material.cc	92.15% <100.00%> (+0.02%)	⬆️

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