fix: handle find() when root node is placeholder comment

Author: LinusBorg

src/vueWrapper.ts

@@ -123,7 +123,7 @@ export class VueWrapper<T extends ComponentPublicInstance>
     const result = this.parentElement['__vue_app__']
       ? // force using the parentElement to allow finding the root element
         this.parentElement.querySelector(selector)
-      : this.element.querySelector(selector)
+      : this.element.querySelector && this.element.querySelector(selector)
 
     if (result) {
       return new DOMWrapper(result)