InventoryGui affected by item duplication in GUIs which use GuiStorageElement

InventoryGui is a library for creating chest GUIs for Bukkit/Spigot plugins. Versions 1.6.1-SNAPSHOT and earlier contain a vulnerability where any plugin using the `GuiStorageElement can allow item duplication when the experimental Bundle item feature is enabled on the server. The vulnerability is resolved in version 1.6.2-SNAPSHOT.