standalone gallery,: add missing screensaver.js

Change-Id: Id670e5f5fdea85b6a34aa6c359815ec9159f3ead

Author: andi34

gallery/index.php

@@ -26,6 +26,7 @@
 
     <script src="<?=$assetService->getUrl('resources/js/preview.js')?>"></script>
     <script src="<?=$assetService->getUrl('resources/js/virtualKeyboard.js')?>"></script>
+    <script src="<?=$assetService->getUrl('resources/js/screensaver.js')?>"></script>
     <script src="<?=$assetService->getUrl('resources/js/core.js')?>"></script>
     <script src="<?=$assetService->getUrl('resources/js/gallery.js')?>"></script>
     <?php if ($config['gallery']['db_check_enabled']): ?>