Fix surveillance camera closing (#28374)

The boilerplate sucks but I haven't thought of something good.

Content.Client/SurveillanceCamera/UI/SurveillanceCameraSetupBoundUi.cs

@@ -31,7 +31,7 @@ protected override void Open()
         _window.OpenCentered();
         _window.OnNameConfirm += SendDeviceName;
         _window.OnNetworkConfirm += SendSelectedNetwork;
-
+        _window.OnClose += Close;
     }
 
     private void SendSelectedNetwork(int idx)
@@ -63,7 +63,8 @@ protected override void Dispose(bool disposing)
 
         if (disposing)
         {
-            _window!.Dispose();
+            _window?.Dispose();
+            _window = null;
         }
     }
 }