Crash in QNSWindow sendEvent

1. Run the demo app on Mac.
2. Click "File->Create QuickView"
3. In a newly created window click "Dock"
4. Then click "Close"
5. Click "qnswindow" menu, hover several items and then click into the central widget on the main window.

Crash trace:
0 QWindow::flags() const qwindow.cpp 688 0x21112dd
1 -[QNSView mouseUp:] qnsview.mm 642 0x6ed1bd0
2 -[NSWindow sendEvent:] -[NSWindow sendEvent:] 0x98741ebb
3 -[QNSWindow sendEvent:] qcocoawindow.mm 129 0x6ec75e4
4 -[NSApplication sendEvent:] -[NSApplication sendEvent:] 0x986e091d
5 -[QNSApplication sendEvent:] qcocoaapplication.mm 183 0x6ee767a
6 -[NSApplication run] -[NSApplication run] 0x985251dc
7 QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) qcocoaeventdispatcher.mm 424 0x6ee03a6
8 QEventLoop::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) qeventloop.cpp 136 0x1915336
9 QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) qeventloop.cpp 212 0x191556b
10 QCoreApplication::exec() qcoreapplication.cpp 1134 0x191a889
11 QGuiApplication::exec() qguiapplication.cpp 1332 0x20ffa78
12 QApplication::exec() qapplication.cpp 2707 0x2aa136b
13 main main.cpp 10 0x46b3