error: invalid conversion from ‘ImGuiID’ {aka ‘unsigned int’} to ‘const char*’ [-fpermissive]

### 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

```console
....../Open3D/cpp/open3d/visualization/gui/Window.cpp:1112:39: error: invalid conversion from ‘ImGuiID’ {aka ‘unsigned int’} to ‘const char*’ [-fpermissive]
1112 | ImGui::IsPopupOpen(w->PopupId)) {
| ~~~^~~~~~~
| |
| ImGuiID {aka unsigned int}
```