INT 21 - Stacker - GET STACVOL FILE SECTORS

	AX = 4404h
	BL = drive number (0 is current drive)
	CX = byte count (i.e., 200h = 1 sector)
	DS:DX -> buffer (see #01529)
Return: Data Buffer contains the number of sectors requested from the
	  STACVOL physical file for the drive specified.