Fix garbled resize with QOpenGLWidget when using multi-sampling.

If you configure QOpenGLWidget to use sampling, the 'resolvedFbo' isn't
updated during resizing. This leads to garbled views.

Change-Id: I9f9265520134bcf12436778773507df936c5fbb6
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>

src/widgets/kernel/qopenglwidget.cpp

@@ -896,6 +896,7 @@ void QOpenGLWidget::resizeEvent(QResizeEvent *e)
     resizeGL(width(), height());
     d->invokeUserPaint();
     d->context->functions()->glFlush();
+    d->resolveSamples();
 }
 
 /*!