UI Toolkit Editor Window Creator Window can be closed before Assets are created resulting in incomplete Editor Window Assets

Steps to reproduce:

1. Open any Project
2. Right click in the Project Browser and select Create > UI Toolkit > Editor Window
3. Enter any string in the C# section and select "Confirm"
4. Close the UI Toolkit Editor Window Creator Window

Actual results: Default Assets are created, they are not automatically opened and they are incomplete and produce errors when opened: "NullReferenceException: Object reference not set to an instance of an object
aa.CreateGUI () (at Assets/Editor/aa.cs:27)
System.Reflection.RuntimeMethodInfo.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at <73ac12a12f9a4ebca156b41ddce95fbe>:0)"

Expected results: Window cannot be closed before the Example Assets are created

Reproducible with versions: 6000.0.63f1, 6000.2.14f1, 6000.3.0f1, 6000.4.0a5, 6000.5.0a2

Tested on (OS): Windows 11