Re-run xeh preInit after terrain switch in Threeden

[PabstMirror]

Switching terrains in 3den will reset missionNamespace.
(either creating a new mission on a new map or loading a save on a new map)

This breaks addons that count on pre-init functions being available in 3den as well as CBA Settings.

On first load into VR
Check var cba_settings is true and cba settings open's normaly.

Switch maps to Stratis:
Check var cba_settings is nil and cba settings opens weird and does not function:

One minor downside to this fix is it stacks a new event handler each run of preInit.
It shouldn't matter because it checks ISPROCESSED, but there might be a better way to do this?

Edit: this is what cba settings opens as after terrain switch