The post_redraw function errors

### 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 i in range(10):
time.sleep(0.2)
self.animate_wave()
if gui.Application.instance.run_one_tick():
self.window.post_redraw()
print("DONE")

As the code above，loops and post_redrwaw function is used to realize animation . If the redraw function is placed in a for loop, after the last loop is executed, python will eixt. If it is placed outside the loop , an error will be reported after the last line is executed.
self.window is gui.Application.instance.create_window("viewer", width, height)