Stop reusing holes in areas IDs

This eliminates the need of iterating the whole list for every protection operations. Note that the highest index isn't cached, i.e. the first or few (if there are many holes) operations would still suffer from the lag.

internal.lua

@@ -83,19 +83,19 @@ function areas:populateStore()
 	self.store_ids = store_ids
 end
 
--- Finds the first usable index in a table
--- Eg: {[1]=false,[4]=true} -> 2
-local function findFirstUnusedIndex(t)
-	local i = 0
-	repeat i = i + 1
-	until t[i] == nil
-	return i
+-- Guarentees returning an unused index in areas.areas
+local index_cache = 0
+local function findFirstUnusedIndex()
+	local t = areas.areas
+	repeat index_cache = index_cache + 1
+	until t[index_cache] == nil
+	return index_cache
 end
 
 --- Add an area.
 -- @return The new area's ID.
 function areas:add(owner, name, pos1, pos2, parent)
-	local id = findFirstUnusedIndex(self.areas)
+	local id = findFirstUnusedIndex()
 	self.areas[id] = {
 		name = name,
 		pos1 = pos1,