This is somewhat of a corner case, where there is a single sub-window,
setViewMode(TabbedView) is called before addSubWindow(), and the latter
is called before show(). The sub-window would be active, i.e.
subwindow->d_func()->isActive is true and QMdiArea::aboutToActivate() is
emitted, but QMA::emitSubWindowActivated() is never called for that
sub-window, resulting in that sub-window shown as
unmaximized/with-a-title-bar instead of as maximized/tabbed as is
expected in TabbedView.
Pick-to: 6.6 6.5
Fixes: QTBUG-114188
Change-Id: Ia7b2cfd07c51867707866a1f99f70129bbdc0e3e
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
c94bcecb22