INT 21 - DOS 2+ - "CWD" - GET CURRENT DIRECTORY
        AH = 47h
        DL = drive number (00h = default, 01h = A:, etc)
        DS:SI -> 64-byte buffer for ASCIZ pathname
Return: CF clear if successful
            AX = 0100h (undocumented)
        CF set on error
            AX = error code (0Fh) (see AH=59h)
Notes:  the returned path does not include a drive or the initial backslash
        many Microsoft products for Windows rely on AX being 0100h on success
        under the FlashTek X-32 DOS extender, the buffer pointer is in DS:ESI
SeeAlso: AH=3Bh,INT 15/AX=DE25h