Prevent from "Call to undefined method rcmail_output_json::add_footer()" error

index.php

@@ -207,6 +207,15 @@ if (empty($RCMAIL->user->ID)) {
         $session_error = true;
     }
 
+    if ($session_error || $_REQUEST['_err'] == 'session') {
+        $OUTPUT->show_message('sessionerror', 'error', null, true, -1);
+    }
+
+    if ($OUTPUT->ajax_call || !empty($_REQUEST['_framed'])) {
+        $OUTPUT->command('session_error', $RCMAIL->url(array('_err' => 'session')));
+        $OUTPUT->send('iframe');
+    }
+
     // check if installer is still active
     if ($RCMAIL->config->get('enable_installer') && is_readable('./installer/index.php')) {
         $OUTPUT->add_footer(html::div(array('style' => "background:#ef9398; border:2px solid #dc5757; padding:0.5em; margin:2em auto; width:50em"),
@@ -218,15 +227,6 @@ if (empty($RCMAIL->user->ID)) {
         ));
     }
 
-    if ($session_error || $_REQUEST['_err'] == 'session') {
-        $OUTPUT->show_message('sessionerror', 'error', null, true, -1);
-    }
-
-    if ($OUTPUT->ajax_call || !empty($_REQUEST['_framed'])) {
-        $OUTPUT->command('session_error', $RCMAIL->url(array('_err' => 'session')));
-        $OUTPUT->send('iframe');
-    }
-
     $plugin = $RCMAIL->plugins->exec_hook('unauthenticated', array('task' => 'login', 'error' => $session_error));
 
     $RCMAIL->set_task($plugin['task']);