Fixed incorrect mail url in response.

web/api/v1/edit/server/index.php

@@ -636,7 +636,7 @@ $result = array(
     'mail_system' => $_SESSION['MAIL_SYSTEM'],
     'antivirus_system' => $_SESSION['ANTIVIRUS_SYSTEM'],
     'antispam_system' => $_SESSION['ANTISPAM_SYSTEM'],
-    'mail_url' => $_SESSION['DB_PMA_URL'],
+    'mail_url' => $_SESSION['MAIL_URL'],
     'pgsql_url' => $_SESSION['DB_PGA_URL'],
     'mail_certificate' => $_SESSION['MAIL_CERTIFICATE'],
     'dns_system' => $_SESSION['DNS_SYSTEM'],