fix: do not throw when combo-box is templatized (#5330) (#5331)

Co-authored-by: Tomi Virkki <tomivirkki@users.noreply.github.com>

Author: vaadin-bot

packages/combo-box/src/vaadin-combo-box-scroller.js

@@ -169,7 +169,9 @@ export class ComboBoxScroller extends PolymerElement {
   }
 
   requestContentUpdate() {
-    this.__virtualizer.update();
+    if (this.__virtualizer) {
+      this.__virtualizer.update();
+    }
   }
 
   scrollIntoView(index) {

packages/combo-box/test/polymer.test.js

@@ -0,0 +1,17 @@
+import { expect } from '@esm-bundle/chai';
+import './not-animated-styles.js';
+import '../vaadin-combo-box.js';
+import { html } from '@polymer/polymer';
+import { templatize } from '@polymer/polymer/lib/utils/templatize.js';
+
+it('should not throw when templatized', () => {
+  // Use Templatizer to create a new combo-box instance
+  const TemplateClass = templatize(html`<vaadin-combo-box></vaadin-combo-box>`);
+  const instance = new TemplateClass();
+  const comboBox = instance.root.querySelector('vaadin-combo-box');
+  // Add the new combo-box instance to the document body
+  expect(() => document.body.appendChild(comboBox)).not.to.throw();
+
+  // Clean up
+  comboBox.remove();
+});