INT 2F U - DOS 3.3+ internal - READ FROM FILE
        AX = 1229h
        BX = file handle
        CX = number of bytes to read
        DS:DX -> buffer
        SS = DOS DS (must be using a DOS internal stack)
Return: as for INT 21/AH=3Fh
Note:   equivalent to INT 21/AH=3Fh, but may only be called when already inside
          a DOS function call
SeeAlso: INT 21/AH=3Fh