This reverts commit 26c37567.
Conflicts:
	vcl/qt5/Qt5Frame.cxx

It caused null pointer dereference during UITest_writer_tests, as seen at
<https://ci.libreoffice.org//job/lo_ubsan/1090/>:

> /sfx2/source/appl/childwin.cxx:654:18: runtime error: member call on null pointer of type 'vcl::Window'
>     #0 0x2b97d4160fa3 in SfxChildWindow::SetWorkWindow_Impl(SfxWorkWindow*) /sfx2/source/appl/childwin.cxx:654:18
>     #1 0x2b97d462ab86 in SfxWorkWindow::CreateChildWin_Impl(SfxChildWin_Impl*, bool) /sfx2/source/appl/workwin.cxx:1350:9
>     #2 0x2b97d463e6bb in SfxWorkWindow::ToggleChildWindow_Impl(unsigned short, bool) /sfx2/source/appl/workwin.cxx:1837:21
>     #3 0x2b97d6eae94d in SfxViewFrame::ToggleChildWindow(unsigned short) /sfx2/source/view/viewfrm.cxx:3080:9
>     #4 0x2b987664316d in SwView::UpdateWordCount(SfxShell*, unsigned short) /sw/source/uibase/uiview/view1.cxx:212:9
>     #5 0x2b9876126a5d in SwTextShell::Execute(SfxRequest&) /sw/source/uibase/shells/textsh1.cxx:1369:9
>     #6 0x2b98760a2391 in SfxStubSwTextShellExecute(SfxShell*, SfxRequest&) /workdir/SdiTarget/sw/sdi/swslots.hxx:2974:1
>     #7 0x2b97d49050f6 in SfxShell::CallExec(void (*)(SfxShell*, SfxRequest&), SfxRequest&) /include/sfx2/shell.hxx:207:35
>     #8 0x2b97d48c27d0 in SfxDispatcher::Call_Impl(SfxShell&, SfxSlot const&, SfxRequest&, bool) /sfx2/source/control/dispatch.cxx:353:13
>     #9 0x2b97d48de12d in SfxDispatcher::Execute_(SfxShell&, SfxSlot const&, SfxRequest&, SfxCallMode) /sfx2/source/control/dispatch.cxx:854:9
>     #10 0x2b97d482ea34 in SfxBindings::Execute_Impl(SfxRequest&, SfxSlot const*, SfxShell*) /sfx2/source/control/bindings.cxx:1063:9
>     #11 0x2b97d4e5cead in SfxDispatchController_Impl::dispatch(com::sun::star::util::URL const&, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&, com::sun::star::uno::Reference<com::sun::star::frame::XDispatchResultListener> const&) /sfx2/source/control/unoctitm.cxx:754:29
>     #12 0x2b97d4e60b5e in SfxOfficeDispatch::dispatchWithNotification(com::sun::star::util::URL const&, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&, com::sun::star::uno::Reference<com::sun::star::frame::XDispatchResultListener> const&) /sfx2/source/control/unoctitm.cxx:239:9
>     #13 0x2b97c6c10b19 in comphelper::dispatchCommand(rtl::OUString const&, com::sun::star::uno::Sequence<com::sun::star::beans::PropertyValue> const&, com::sun::star::uno::Reference<com::sun::star::frame::XDispatchResultListener> const&) /comphelper/source/misc/dispatchcommand.cxx:60:9
>     #14 0x2b980472020c in UITest::executeCommand(rtl::OUString const&) /vcl/source/uitest/uitest.cxx:22:12
[...]

Change-Id: I276684a5617bfec3803b195af59c51735bfa470a