PowerDNS plugin: DNSSEC bug fix

There is a bug in https://git.ispconfig.org/ispconfig/ispconfig3/-/blob/develop/server/plugins-available/powerdns_plugin.inc.php#L505

When DNS zone is just created (not updated), all values in $data['old'] are null, including dnssec_wanted. So result of $data['old']['dnssec_wanted'] === 'N' will be false. This is how this line should look like:

		if ($data['new']['dnssec_wanted'] === 'Y' && (is_null($data['old']['dnssec_wanted']) || $data['old']['dnssec_wanted'] === 'N')) {