Fixed editor JavaScript error in TemplateManager

- Caused when loading the editor with no templates in the system.
- Tried to init a search box that did not exist.

resources/js/components/template-manager.js

@@ -56,6 +56,10 @@ class TemplateManager {
 
     setupSearchBox() {
         const searchBox = this.elem.querySelector('.search-box');
+
+        // Search box may not exist if there are no existing templates in the system.
+        if (!searchBox) return;
+
         const input = searchBox.querySelector('input');
         const submitButton = searchBox.querySelector('button');
         const cancelButton = searchBox.querySelector('button.search-box-cancel');