Validation bug in DNS DMARC

Summary

When trying to create a DMARC record for a domain where the DKIM is configured via a CNAME record ISPConfig errors with dmarc_no_dkim_txt. As this is a valid setup (see O365 docs for example) the validation function needs to be corrected. Reference thread in the forums: https://forum.howtoforge.com/threads/configuring-dkim-and-dmarc-with-office-365.91120/#post-449340

Steps to reproduce

1. Create a CNAME that point to the DKIM Record
2. Trying adding a DMARC Record
3. Result: Error dmarc_no_dkim_txt

Correct behaviour

The validation should not check, as it is possible that the record is not configured in the same zone.

Proposed fix

The file in question is interface/web/dns/dns_dmarc_edit.php lines 229-236:

     // DMARC requieres at least one active dkim-record...
                $sql = "SELECT * FROM dns_rr
                                        LEFT JOIN dns_soa ON (dns_rr.zone=dns_soa.id)
                                        WHERE dns_soa.origin = ? AND dns_rr.name LIKE ? AND type='TXT' AND data like 'v=DKIM1;%' AND dns_rr.active='Y'";
                $temp = $app->db->queryAllRecords($sql, $soa['origin'], '%._domainkey%');
                if (empty($temp)) {
                        if (isset($app->tform->errorMessage )) $app->tform->errorMessage = '<br/>' . $app->tform->errorMessage;
                        $app->tform->errorMessage .= $app->tform->wordbook['dmarc_no_dkim_txt'].$email;
                }