INT 15 - TopView - SEND MESSAGE - "ADDR" - GET HANDLE OF MESSAGE SENDER
        AH = 12h
        BH = 03h
        BL = object
            00h mailbox handle in DWORD on top of stack
            02h sender of last msg read from mailbox (task's handle on stack)
            03h sender of last msg read from current task's mailbox
Return: DWORD on stack is task handle of message sender
SeeAlso: AH=12h/BH=83h