Combine GO object fields and format_txt.

def __init_go2nt_w_usr(self, gos_all, usr_go2nt, prt_flds_all):
        """Combine GO object fields and format_txt."""
        assert usr_go2nt, "go2nt HAS NO ELEMENTS"
        from goatools.nt_utils import get_unique_fields
        go2nts = [usr_go2nt, self.gosubdag.go2nt, self._get_go2nthdridx(gos_all)]
        usr_nt_flds = next(iter(usr_go2nt.values()))._fields # Get any single value from a dict
        flds = get_unique_fields([usr_nt_flds, prt_flds_all])
        go2nt = get_dict_w_id2nts(gos_all, go2nts, flds)
        return self._init_go2nt_aug(go2nt)