Fix crashing if null itemstack enchant when player is hacking

mods/ITEMS/mcl_enchanting/engine.lua

@@ -6,6 +6,9 @@ function mcl_enchanting.is_book(itemname)
 end
 
 function mcl_enchanting.get_enchantments(itemstack)
+	if not itemstack then
+		return({})
+	end
 	return minetest.deserialize(itemstack:get_meta():get_string("mcl_enchanting:enchantments")) or {}
 end