Inconsistent CloudLayer texture fallback assignment (noticeable on Triton)

When attempting to mod a planet while leaving all the vanilla texture paths in place, normally the program detects when a mod doesn't have a reference to said texture and then defaults to load the unmodded texture.

Whereas with all the different voxel textures, you can use the default paths and the game figures out which unmodded paths you want to use after it fails to find them in the mod's folder, with the clouds this is not always the case.

With Triton, instead of having a sky with a couple layers of white clouds in it, you're greeted with a pitch black sky.

To get clouds to work again, it requires copying the cloud's 40+MB alpha mask texture from the SE base directory into the mod:

\Textures\Models\Environment\Sky\Landsky_texture_alphamask.dds

To reproduce, please do the following:

New folder in mods folder ("fallbackdemo"), add "Data" folder to that one.

Copy these three files to the "Data" folder from the SE game steamapps "Data" folder:

"PlanetGeneratorDefinitions.sbc" -> "Override-PlanetGeneratorDefinitions.sbc"

"Pertam.sbc" -> "Override-Pertam.sbc"

"Triton.sbc" -> "Override-Triton.sbc"

For a working sample on the workshop that follows those three instructions with the most up-to-date version of the game's sbc files as an example, here is a link:

https://steamcommunity.com/sharedfiles/filedetails/?id=2403341330

In the attached pictures using the above mod, you'll notice that the Earthlike is completely unaffected and looks the same between normal unmodded gameplay and that when modded with the demo mod.

Whereas Triton looks completely different -- the clouds are gone and even the sun is darkened out.