Updated material mask in Atmosphere sample to fix libpng warning
Updated material mask in Atmosphere sample to fix libpng warning

DiligentGraphics/DiligentSamples,DiligentGraphics/DiligentSamples,DiligentGraphics/DiligentSamples,DiligentGraphics/DiligentSamples,DiligentGraphics/DiligentSamples,DiligentGraphics/DiligentSamples