fix(WidgetManager): Unsubscribe to events when widgetManager is deleted

If the widgetManager is deleted, it does not unsubscribe to events. If an event is triggered
(svgSetSize for example), the vizualization will crash since widgetManager does no longer exist.

Author: pchoisel

Sources/Widgets/Core/WidgetManager/index.js

@@ -461,6 +461,14 @@ function vtkWidgetManager(publicAPI, model) {
     }
     return false;
   };
+
+  const superDelete = publicAPI.delete;
+  publicAPI.delete = () => {
+    while (subscriptions.length) {
+      subscriptions.pop().unsubscribe();
+    }
+    superDelete();
+  };
 }
 
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