API GetInventoryItemID

Returns the item ID for an equipped item.
 itemId, unknown = GetInventoryItemID(unit, invSlotId)
==Arguments==
:;unit: : UnitId - The unit whose inventory is to be queried.
:;invSlotId: : InventorySlotId - to be queried, obtained via GetInventorySlotInfo.
==Returns==
:;itemId: - item id of the item in the inventory slot; nil if there is no item.
:;unknown: - ?