fix: sanitizzato $_GET['firstuse'] in update.php per prevenire attacchi XSS

Author: lucasalva87

include/init/update.php

@@ -78,7 +78,7 @@
 
             echo '
                 <script>
-                    $("#result").load("index.php?action=do_update&firstuse='.$_GET['firstuse'].'");
+                    $("#result").load("index.php?action=do_update&firstuse='.htmlspecialchars($_GET['firstuse'], ENT_QUOTES).'");
                 </script>';
         } else {
             // Failure