[macOS]: When triggering a pan gesture and then deleting the widget that it is intended for can cause a crash

[macOS]: When triggering a pan gesture and then deleting the widget that it is intended for can cause a crash. What happens is that it will delete the widget the gesture has started the timer for, yet the timer is not removed and therefore it ends up crashing when it tries to deliver it.

This happens on macOS as it uses QMacPanGestureRecognizer. When it starts a gesture it has a QBasicTimer which is set to the widget as the target to timeout in 300 ms. If the widget is deleted before this timer fires it can crash due to the fact that the target is no longer valid.