INT 21 - DOS 2+ - GET FILE ATTRIBUTES
        AX = 4300h
        DS:DX -> ASCIZ filename
Return: CF clear if successful
            CX = file attributes (see AX=4301h)
            AX = CX (DR-DOS 5.0)
        CF set on error
            AX = error code (01h,02h,03h,05h) (see AH=59h)
Notes:  under the FlashTek X-32 DOS extender, the filename pointer is in DS:EDX
        under DR-DOS 3.41 and 5.0, attempts to change the subdirectory bit are
          simply ignored without an error
SeeAlso: AX=4301h,AX=4310h,AH=B6h,INT 2F/AX=110Fh

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