MDL-43140 mnet: display header after redirects to avoid warning

admin/mnet/access_control.php

@@ -16,8 +16,6 @@ require_login();
 
 admin_externalpage_setup('ssoaccesscontrol');
 
-echo $OUTPUT->header();
-
 if (!extension_loaded('openssl')) {
     print_error('requiresopenssl', 'mnet');
 }
@@ -118,6 +116,8 @@ if ($form = data_submitted() and confirm_sesskey()) {
     exit;
 }
 
+echo $OUTPUT->header();
+
 // Explain
 echo $OUTPUT->box(get_string('ssoacldescr','mnet'));
 // Are the needed bits enabled?