fix theme upload error bug

[popstk]

        diskFile, err := os.OpenFile(diskFilePath, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o444)
	if !errors.Is(err, os.ErrExist) {
		return nil, xerr.WithStatus(err, xerr.StatusInternalServerError).WithMsg("create file error")
	}

if err == nil