tdf#120786: show undocked toolbar only when it's ready

in SetAlwaysOnTop set window flags only, don't show the widget yet
(it'll be shown later, when it can be painted in full)

Change-Id: I5e855f1ebba1eb9985744ece055a0f141e965940
Reviewed-on: https://gerrit.libreoffice.org/67739Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>
Tested-by: Katarina Behrens <Katarina.Behrens@cib.de>

vcl/qt5/Qt5Frame.cxx

@@ -609,7 +609,6 @@ void Qt5Frame::SetAlwaysOnTop(bool bOnTop)
         pWidget->setWindowFlags(flags | Qt::CustomizeWindowHint | Qt::WindowStaysOnTopHint);
     else
         pWidget->setWindowFlags(flags & ~(Qt::CustomizeWindowHint | Qt::WindowStaysOnTopHint));
-    pWidget->show();
 }
 
 void Qt5Frame::ToTop(SalFrameToTop nFlags)