Bug Fix for : Falling through terrain #2337

# Description:
The issue identified in #2337 is a bit too big and complex to be fixed easily so this patch attempts to apply a few bandages instead.
Really it needs the terrain system writing anew.

# The "Fix":
The actual fix is found in `Space.cpp` Line 733 as identified by @lwho, this "fix" simply doubles the height that we start checking for collision at. It is a *hack* and not a very nice magic number one but it should catch most cases.

# Other stuff:
I added a check in `GeoPatchJobs.cpp` to catch cases where the terrain height is outside of it's acceptable range.
The functions defined in `TerrainNoise.h` had name which made debugging and fathoming out their purpose very difficult so I've renamed the variables used to more commonly acceptable versions... instead of `jizm` for example.

It looks like I accidentally pulled in my aborted initial attempt to fix `TerrainHeightBarrenRock2.cpp` too. Not sure what the best way to remove that is.

# Doubts:
I think that asserts get compiled in when using MinGW or GCC, possibly also on OSX so the assert in `GeoPatchJobs.cpp` might want guarding with `#ifdef _DEBUG` or whatever our Pi equivalent is.