Description:

`spinOnce` method used to work great in while loops to enable animation in a Viz window by doing:

```
while not v.wasStopped():
v.spinOnce(1, True)
```

Which is how it is done in the OpenCV Tutorials for viz in C++.
Now the window freezes and no mouse nor keyboard event is recognized thus impossible to cleanly close the windows or rotate the camera in the scene.
Sometimes it leads to a X server error:

X Error of failed request: BadWindow (invalid Window parameter)
Major opcode of failed request: 38 (X_QueryPointer)
Resource id in failed request: 0x5800002
Serial number of failed request: 1036
Current serial number in output stream: 1036

The `spin` method works though, but is not meant for while loops.

Steps to reproduce:
- Use the latest version of opencv, python-opencv and vtk installed using pacman
- Run the following in python 3.9.7:

```
import cv2

v = cv2.viz.Viz3d_create("Viz Demo")
v.showWidget("axes", cv2.viz_WCameraPosition(1))

while not v.wasStopped():
v.spinOnce(1, True)
```

- Window freezes, and does not respond to keyboard or mouse events.