Windows: Uninitialized value when calling GetWindowPlacement

According to documentation:
http://msdn.microsoft.com/en-us/library/windows/desktop/ms633518%28v=vs.85%29.aspx

Before calling GetWindowPlacement, set the length member to sizeof(WINDOWPLACEMENT). GetWindowPlacement fails if lpwndpl-> length is not set correctly.

In Qt 4.x, this is uninitialized in QWidgetPrivate::setGeometry_sys()