Fixes for some random maps.
- Hellas_biome isn't a RM but as a JSON script it does load, and then silently fails on mapgen. Explicitly fail.
- Fix player.js when a valid position cannot exist.
- Fix unknown.js when landscape isn't set in the settings.
Reported by: vladislavbelov
Differential Revision: https://code.wildfiregames.com/D4147