Substrate's coverage node does not skip unlit emissive part which have no coverage

Substrate's coverage node doesn't seem to cull masked pixels of unlit emissive slabs. This is an important optimization when using masked unlit particles. When using a lit slab, the instructions for masked pixels do get culled as expected

• Open the attached project and test level
• Enter "stat gpu" in the console and observe the frame time taken by "Translucency"
• Open the M_SubstrateTest material, set the Static Switch node to True to reduce the coverage of the material and save the material
• Observe in the stats that there is almost no difference in the time taken up by "Translucency", while it is expected that this should go down to zero (as is the case for lit materials, where Substrate can early-out of shader instructions for pixels without coverage)