Incorrect texturing for add-ons about celestia

[ajtribick]

This comes down to the use of Mesh "" in the Auroral Oval - this is now detected as an invalid filename and thus the Mesh declaration gets ignored, leading to the object being created as a sphere that intersects the actual Earth leading to the patterns. Previously this declaration would be accepted, resulting in the geometry having an invalid resource and thus not being rendered.

One fix is to remove the Mesh declaration, decrease the radius of Auroral Oval and increase the cloud height. This also has the bonus effect of not logging an error when it fails to load the nonexistent mesh.