fix: prevent runtime error when component will unmount

[lksnmnn]

This change will prevent a crash, when react calls the componentWillUnmount lifecycle method upon unmounting the <Container> component. Somehow we managed to reach a state, where this.container is already null thus throwing an error when trying to call dispose().

TypeError: Cannot read properties of null (reading 'dispose')

We are using react v18.2.0.