QOpenGLWindow can crash with older than OpenGL 3.0

To reproduce, run anything with QOpenGLWindow. For example:

#include <QApplication>
#include <QOpenGLWindow>
int main(int argc, char** argv) {
 QApplication::setAttribute(Qt::AA_UseDesktopOpenGL);
 QApplication app(argc, argv);
 QOpenGLWindow w;
 w.show();
 return app.exec();
}

This crashes when QOpenGLWindowPrivate::beginPaint() calls glBindFramebuffer() in some systems. The function might not be available until OpenGL 3.0 or if ARB_framebuffer_object/EXT_framebuffer_object extension is found.

https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glBindFramebuffer.xhtml