Stops a single press of the pick up key from picking up or dropping more than one item. Bits 0-1 are set by HandlerPickupItem when an item is picked up, and bit 1 is set by HandlerBlank when the inventory is dropped. While either bit is set the key does nothing. Bit 1 is reset by ClearPickupFlag and HandlerBlank_KeyUp when the key is not pressed, and bit 0 is reset by HandlerBlank_Finish.