"Invalid operation" error in resizeGL after window closed

• Window 10 64-bit
• Python 3.8
• PySide 6.4.2
• PyOpenGL 3.1.6

When I close the window, I get an "Invalid operation" error in resizeGL() on the line with the glViewport() function.

```python
import sys

from OpenGL.GL import *
from PyQt6.QtCore import Qt
from PyQt6.QtOpenGL import QOpenGLWindow
from PyQt6.QtWidgets import QApplication

class OpenGLWindow(QOpenGLWindow):

    def _init_(self):
        super()._init_()

    def initializeGL(self):
        glClearColor(0.2, 0.2, 0.2, 1)

    def resizeGL(self, w, h):
        glViewport(0, 0, w, h)

    def paintGL(self):
        glClear(GL_COLOR_BUFFER_BIT)

if _name_ == "_main_":
    QApplication.setAttribute(Qt.ApplicationAttribute.AA_UseDesktopOpenGL)
    app = QApplication(sys.argv)
    w = OpenGLWindow()
    w.show()
    sys.exit(app.exec())
```

Debugging details:

```
Traceback (most recent call last):
  File "E:_Projects\OpenGL\basic-examples\animations\set-swap-interval-opengl21-pyqt6-python\opengl_window.py", line 15, in resizeGL
    glViewport(0, 0, w, h)
  File "E:\ProgramFiles\Python\Python38\lib\site-packages\OpenGL\error.py", line 230, in glCheckError
    raise self._errorClass(
OpenGL.error.GLError: GLError(
        err = 1282,
        description = b'invalid operation',
        baseOperation = glViewport,
        cArguments = (0, 0, 160, 160)
)
```