Bugs found with Server.addArea / Server.removeArea

I'm currently working on my own LandClaim plugin and noticed some things:

- if you use `area.setPlayerPermission` before `Server.addArea`, the permissions are not persisted to the database.
- if you use `Server.removeArea` before removing all player permissions from the area, the permissions stay in the database with no valid area.

Might not be critical but it cost me much time to figure this out