Broken wasteland skybox

It worked before™ but it doesn't anymore:

```
Warn: cube map face 'env/wasteland/wasteland_rt' has DXTn compression, cube map unusable 
Warn: could not find cubemap 'env/wasteland/wasteland' for outer skybox in shader 'textures/perseus_env/sky' 
```

I first reproduced it on atcshd that ships wasteland, but one can reproduce it with stock assets as perseus ships a copy of wasteland.