File 업로드 dialog

*-- 업로드 파일명 구하기
CALL METHOD CL_GUI_FRONTEND_SERVICES=>FILE_OPEN_DIALOG
    EXPORTING                           " 생략가능
      window_title      = lv_title      " 생략가능
      default_filename  = lv_fname      " 생략가능
      initial_directory = lv_path       " 생략가능
  CHANGING
    FILE_TABLE              = lv_filetable
    RC                      = lv_answer
    USER_ACTION             = lv_answer.