Added NPC's counter adapted to the API

- It seems in fact that sometimes, when you give the fourth diamond to a NPC, it does not follow
  because you're too close to it. (engine's entity issue, or algorythm issue, but not really one
  since you just have to move in 99% of the cases to make the NPC follow you)

mods/mobs/npc.lua

@@ -87,15 +87,14 @@ mobs:register_mob("mobs:npc", {
 			local pos = self.object:getpos()
 			pos.y = pos.y + 0.5
 			minetest.add_item(pos, {name = mobs.npc_drops[math.random(1,#mobs.npc_drops)]})
---[[		elseif item:get_name() == "default:diamond" then
+		elseif item:get_name() == "default:diamond" then
 			self.diamond_count = (self.diamond_count or 0) + 1
 			if not minetest.setting_getbool("creative_mode") then
 				item:take_item()
 				clicker:set_wielded_item(item)
 			end
 			if self.diamond_count < 4 then return end
-]]--
-		else
+
 			if self.owner == "" then
 				self.owner = clicker:get_player_name()
 			else