INT 21 - DOS 3.3+ - "FFLUSH" - COMMIT FILE
        AH = 68h
        BX = file handle
Return: CF clear if successful
            all data still in DOS disk buffers is written to disk immediately,
              and the file's directory entry is updated
        CF set on error
            AX = error code (see AH=59h)
SeeAlso: AH=6Ah,INT 2F/AX=1107h