Windows mobile: posted events don't get sent until user clicks main window

Results from QTBUG-8972.

See the attached sample code. QCoreApplication::sendPostedEvents doesn't get called for the 2nd emitted signal.
Because in the function qt_GetMessageHook in qeventdispatcher_win.cpp, the call to GetQueueStatus(QS_TIMER) almost always returns true.

This is the case, because the implementation of Windows mobile menus seems to use WM_TIMER messages internally, which are seen by GetQueueStatus, but will never reach our application. Thus, we don't post the WM_QT_SENDPOSTEDEVENTS message. (Every Qt application on Win mobile has a default menu, even if its not visible.)

When the user clicks into the window, we receive a mouse message and call qt_GetMessageHook again.