Fixed #21825 -- gis compiler uses self instead of qn for as_sql()

        This routine is overridden from Query to handle customized selection of

        geometry columns.

        """

        qn = self.quote_name_unless_alias

        qn = self

        qn2 = self.connection.ops.quote_name

        result = ['(%s) AS %s' % (self.get_extra_select_format(alias) % col[0], qn2(alias))

                  for alias, col in six.iteritems(self.query.extra_select)]