Refactor condition tests in shadow related code

[xezon]

This change refactors some conditions in shadow related code to match our guidelines.

It does not change functionality.

[codecov-commenter]

Codecov Report

Attention: 29 lines in your changes are missing coverage. Please review.

Comparison is base (cfa005f) 2.53% compared to head (5fd6a95) 2.53%.

Files	Patch %	Lines
src/w3d/renderer/dx8vertexbuffer.cpp	0.00%	16 Missing ⚠️
...orm/w3dengine/client/shadow/w3dprojectedshadow.cpp	0.00%	10 Missing ⚠️
...tform/w3dengine/client/shadow/w3dbuffermanager.cpp	0.00%	2 Missing ⚠️
...rm/w3dengine/client/shadow/w3dvolumetricshadow.cpp	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1102   +/-   ##
========================================
  Coverage     2.53%    2.53%           
========================================
  Files          949      949           
  Lines       110299   110299           
  Branches     18881    18881           
========================================
  Hits          2800     2800           
  Misses      107095   107095           
  Partials       404      404           

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