Crash in QGestureManager::~QGestureManager during application exit after unregister/register

When certain order calls to QGestureManager::registerRecognizer / unregisterRecognizer and QWidget::grabGesture is made, QGestureManager::~QGestureManager segfaults.

This happens for example on Windows platform:
1) QGM registers default and platform specific pan gesture recognizers
2) Application creates, for example, a QGraphicsView (which has an QAbstractScrollArea that grabs PanGesture)
3) Application unregisters the Pan recognizers
4) Application registers a custom Pan recognizer

Test case attached.