Patch to fix terrain textures

[GartzenDeHaes]

Hi, to get the terrain textures to render, change CellManager.cs lines 586- 591 to

splat = new TerrainLayer();
splat.diffuseTexture = texture;
splat.smoothness = 0.075f;
splat.metallic = 0.05f;
splat.specular = Color.black;
splat.maskMapTexture = TextureManager.CreateMaskTexture(splat.metallic, 1, 0, splat.smoothness);

The key part is that the green channel of the mask texture is AO (Ambient Occlusion). Setting it to zero makes the terrain dark.

[demonixis]

Thanks a lot, don't hesitate to do a PR otherwise I can update the code myself