Resolves: tdf#90155 don't hide+show window before initial show completes

(cherry picked from commit c4bae028)

Change-Id: I16f6fb4ef025f2e464ca581fc348e8dd18981285

vcl/source/window/floatwin.cxx

@@ -637,10 +637,6 @@ void FloatingWindow::SetTitleType( FloatWinTitleType nTitle )
 
 void FloatingWindow::StartPopupMode( const Rectangle& rRect, FloatWinPopupFlags nFlags )
 {
-    // avoid flickering
-    if ( IsVisible() )
-        Show( false, SHOW_NOFOCUSCHANGE );
-
     if ( IsRollUp() )
         RollDown();