P0-B1: Part 1021: Debugging, Improvements

The multi-threaded scanning function for terrain objects is working, and the entire system seems to be quite solid.

While working on this I also found, and fixed, some other long-standing bugs within the terrain and ground cover systems, which I also fixed.

There is one bug remaining within this system now, and that is that when the scanning function runs at the same time that the terrain itself is subdividing (Such as when the player is moving) the scanning function can fail.

This is likely due to the scanning function being multi-threaded, and accessing the same data that the terrain subdivision function is using.

Other than that, this feature seems to work well.