How to update geometry data without closing the visualizer.

### 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

I want to keep the visualizer on and just update the value, what should I do? Below is the code I wrote. I created a visualizer window with threads when running the ShowVisualizer function, and after the first run, I made it like that to update only certain values at every run, but I can't get out of the function. Is there an example to refer to?