Handle closing of ContextWindow correct

Elwig/Windows/ContextWindow.cs

@@ -1,5 +1,5 @@
 using Elwig.Helpers;
-using System.ComponentModel;
+using System;
 using System.Windows;
 
 namespace Elwig.Windows {
@@ -11,9 +11,9 @@ namespace Elwig.Windows {
             Context = new();
         }
 
-        protected override void OnClosing(CancelEventArgs evt) {
+        protected override void OnClosed(EventArgs evt) {
+            base.OnClosed(evt);
             Context.Dispose();
-            base.OnClosing(evt);
         }
     }
 }