Buy map when needed

Buy map button availability depends on the fact that there are still unexplored parts of the map.

script/events/room.js

@@ -434,18 +434,7 @@ Events.Room = [
 						text: _('buy map'),
 						cost: { 'fur': 200, 'scales': 10 },
 						available: function() {
-							var mask = $SM.get('game.world.mask');
-							var dark = false;
-							loop:
-							for(var i = 0; i < mask.length; i++) {
-								for(var j = 0; j < mask[i].length; j++) {
-									if(!mask[i][j]) {
-										dark = true;
-										break loop;
-									}
-								}
-							}
-							return dark;
+							return !World.seenAll;
 						},
 						notification: _('the map uncovers a bit of the world'),
 						onChoose: World.applyMap