Check if this group ID is valid.

def is_group_valid(self, groupID):
        """
        Check if this group ID is valid.
        """
        cur = self.conn.cursor()
        cur.execute('SELECT * FROM groups WHERE id=? LIMIT 1', [groupID])
        results = cur.fetchall()
        cur.close()

        logging.debug('is_group_valid(groupID={}) => {}'.format(groupID, True if len(results) else False))
        return len(results) > 0