INT 21 - DOS 3.2+ - IOCTL - GET LOGICAL DRIVE MAP

	AX = 440Eh
	BL = drive number (00h=default,01h=A:,etc)
Return: CF set on error
	    AX = error code (01h,0Fh) (see #01680 at AH=59h/BX=0000h)
	CF clear if successful
	    AL = 00h block device has only one logical drive assigned
		 1..26 the last letter used to reference the drive (1=A:,etc)
Notes:	DR DOS 3.41-5.0 DRIVER.SYS does not support drive mapping and thus
	  always returns AL=00h; Windows NT 4.0 also always returns AL=00h
	in addition to the normal operation, if Stacker is installed, this
	  call also sets the volume number at offset 58h in the Stacker
	  device driver (DR DOS 3.41-5.0 only; use AX=4408h otherwise)
	  (see AX=4404h"Stacker",INT 25/AX=CDCDh)
SeeAlso: AX=4408h,AX=440Fh,INT 2F/AX=122Bh