Testing and setting SESSION.error and SESSION.message if they're not defined

www/index.php

@@ -42,6 +42,12 @@ $f3->set('ONERROR', function ($f3) {
     // If there is any problem, replace the current csrf
     $csrf = md5(rand());
     $f3->CSRF = $csrf;
+
+    // If neither error or message are set, define them
+    if (!$f3->exists('SESSION.message'))
+        $f3->push('SESSION.message', '');
+    if (!$f3->exists('SESSION.error'))
+        $f3->push('SESSION.error', '');
     $f3->get('container')['session']->set('csrf', $csrf);
 
     while (ob_get_level()) {