Qt::Tool widget crashes when performing Exposé or Mission Control gestures with mouse down.

Tested using a trackpad, not sure if you can reproduce using other input devices.

In a widget with the Qt::Tool window flag ("Tool Widget" in the attached example):

1. press and hold finger down, then swipe up with three fingers;
2. release all fingers at the end of the gesture.

The application crashes.

Cause of the crash:

• NSEvent locationInWindow property for the LeftMouseUp event returns an NSPoint with NaN values;
• QGuiApplicationPrivate::processMouseEvent detects this event changes the cursor position and buttons, so splits it in two, sending the position change first;
• QGuiApplicationPrivate::processMouseEvent stores the last event position and uses it for the check above, however NaN values cannot be compared and so QGuiApplicationPrivate::processMouseEvent is called recursively until the buttons change;
• The application then crashes with EXC_BAD_ACCESS.