Avoid sending landmap data for Falklands.

This is too damn slow. A possible solution is explained in the comment,
but we shouldn't tackle that until we're sure the rest of the game runs
okay.

game/server/mapzones/models.py

@@ -20,6 +20,10 @@ class MapZonesJs(BaseModel):
     class Config:
         title = "MapZones"
 
+    @classmethod
+    def empty(cls) -> MapZonesJs:
+        return MapZonesJs(inclusion=[], exclusion=[], sea=[])
+
 
 class UnculledZoneJs(BaseModel):
     position: LeafletPoint