Not all sidebar entries have the "classes" attribute

Signed-off-by: Morris Jobke <hey@morrisjobke.de>

apps/files/templates/appnavigation.php

@@ -64,7 +64,7 @@
  * @return int Returns the pinned value
  */
 function NavigationListElements($item, $l, $pinned) {
-	strpos($item['classes'], 'pinned') !== false ? $pinned++ : '';
+	strpos($item['classes'] ?? '', 'pinned') !== false ? $pinned++ : '';
 	?>
 	<li
 		data-id="<?php p($item['id']) ?>"