@brief Retrieves the ref handle from the worn object.
@param a_equipSlot The slot the object is equipped to.
@return Returns INVALID_REFHANDLE on error, else returns the ref handle for the worn object.
@notes Valid equip slots:
0 - LeftHand
1 - RightHand
2 - Shield
3 - Head
4 - Chest
5 - Boots
6 - Gloves