Handle intermittently closed edit fields

[ci skip]

frontend/app/components/wp-edit-form/work-package-edit-form.ts

@@ -204,7 +204,7 @@ export class WorkPackageEditForm {
 
     fields.forEach((name:string) => {
       const handler = this.activeFields[name];
-      handler.deactivate();
+      handler && handler.deactivate();
     });
   }