Issue #3517059: Error when accessing search results page if index is disabled

Closes #3517059

search_api.module

@@ -600,6 +600,9 @@ function search_api_form_views_exposed_form_alter(&$form, FormStateInterface $fo
     // not always actually saved in the storage, if the admin didn't change
     // their settings.)
     $query = $query_plugin->getSearchApiQuery();
+    if (empty($query)) {
+      return;
+    }
     $display_id = $query->getSearchId(FALSE);
     $facet_source_id = str_replace(':', '__', 'search_api:' . $display_id);
     $facet_source = \Drupal::entityTypeManager()