Issue #3415109 by azuryte: Update pager preprocess hook

ui_suite_bootstrap.theme

@@ -41,11 +41,14 @@ function ui_suite_bootstrap_preprocess_breadcrumb(array &$variables): void {
  * Implements hook_preprocess_HOOK() for 'pager'.
  */
 function ui_suite_bootstrap_preprocess_pager(array &$variables): void {
+  if (!isset($variables['items'])) {
+    return;
+  }
   $before = LinksSettingType::normalize(array_filter([
-    $variables["items"]["first"] ?: [],
-    $variables["items"]["previous"] ?: [],
+    $variables['items']['first'] ?: [],
+    $variables['items']['previous'] ?: [],
   ]));
-  $pages = LinksSettingType::normalize($variables["items"]["pages"]);
+  $pages = LinksSettingType::normalize($variables['items']['pages'] ?? []);
   unset($pages[$variables["current"] - 1]["url"]);
   $after = LinksSettingType::normalize(array_filter([
     $variables["items"]["next"] ?: [],