QGLContext::makeCurrent() crashes due to d->guiGlContext being null

On destruction of a Widget derived from QGLWidget a call to makeCurrent() within the Widget's destructor on the widget resulted in a SEGFAULT.

The crash occurs on line 3586:

if (d->guiGlContext->makeCurrent(widget->windowHandle())) {

due to d->guiGlContext being null.

There are quite a few other places where d->guiGlContext is not checked for being a null ptr within this file.

I've also looked at the 5.15.4 and there are very few checks for d->guiGlContext being a null ptr.

This problem does not occur if the Widget is derived from QOpenGLWidget.