InventoryGUI vulnerable to item duplication via Bundle items when using GuiStorageElement

InventoryGui is a library for creating chest GUIs for Bukkit/Spigot plugins. Versions 1.6.3-SNAPSHOT and earlier contain a vulnerability where GUIs using GuiStorageElement can allow item duplication when the experimental Bundle item feature is enabled on the server. The vulnerability is resolved in version 1.6.4-SNAPSHOT.