INT 15 - DESQview/X 1.02+ - DVDOS4GX.DVR - CHECK IF ??? MAILBOX OWNED           
	AX = BFDEh
	BX = 0016h
	CX = index of ??? mailbox
		(0000h-0004h valid, but no range checking done)
Return: AX = status
	    0000h no one owns mailbox
	    0001h mailbox has an owner
	BX destroyed
SeeAlso: AX=BFDEh/BX=0015h,AX=BFDEh/BX=0017h