O3DVisualizer crashes on quit window

This following code would crash randomly on quit window. It happens even with only one window added to the application but seems to be more reproducible with 2+ windows. `vis.reset` doesn't seem to help.

https://github.com/isl-org/Open3D/issues/3878 might be related.

```
int main(int argc, char *argv[]) {
gui::Application::GetInstance().Initialize();
{
auto vis0 = std::make_shared(
"Open3D - Multi-Window Demo", WIDTH, HEIGHT);
gui::Application::GetInstance().AddWindow(vis0);
vis0.reset();
}

{
auto vis = std::make_shared(
"Open3D - Multi-Window Demo", WIDTH, HEIGHT);
gui::Application::GetInstance().AddWindow(vis);
vis.reset();
}
gui::Application::GetInstance().Run();
return 0;
}
```

Also do we support the following pattern?
```
gui::Application::GetInstance().Initialize();
...
...
gui::Application::GetInstance().Run();
...
gui::Application::GetInstance().Initialize();
...
...
gui::Application::GetInstance().Run();

```