Improve rendering for cells without data for Distant Terrain
Currently if the cell has no data, we consider it as having the plain square terrain at height -2048 and the _land_default.tga texture.
We create such data on the fly foe the cells grid near player (depending on ECLD setting value, I suppose).
Unfortunately, if a user does not use a water shader with refraction, with a large viewing distance (e.g. with Distant Terrain) he will see the underwater terrain in the "viewing distance" radius, including holes where there is no data (vanilla water just was not designed for huge viewing distances).
The only reliable way I see is to limit underwater visibility without refraction too, but I do not know if it even possible with the fixed function pipeline.