How to handle widget callback failures?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

For example a slider is used and i have a callback set to be executed on value change as `my_slider.set_on_value_change(my_callback)`. If there is a change of value and there a condition within the callback to not use that particular value or the callback fails to execute , then would it possible to automatically reset the slider value to the previous value that was present before it was moved?