Resolves: tdf#120885 Crash on choosing 'more styles'

switching to the sidebar destroys the control currently active,
just post the event to happen on the next event loop

Change-Id: I3e9b629821fa43d8f29e419e72f66ed46d72fdbb
Reviewed-on: https://gerrit.libreoffice.org/65543
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
(cherry picked from commit 93f26a66)

svx/source/tbxctrls/tbcontrl.cxx

@@ -176,6 +176,7 @@ private:
     static bool     AdjustFontForItemHeight(OutputDevice* pDevice, tools::Rectangle& rTextRect, long nHeight);
     void            SetOptimalSize();
     DECL_LINK( MenuSelectHdl, Menu *, bool );
+    DECL_STATIC_LINK(SvxStyleBox_Impl, ShowMoreHdl, void*, void);
 };
 
 class SvxFontNameBox_Impl : public FontNameBox
@@ -428,6 +429,16 @@ IMPL_LINK( SvxStyleBox_Impl, MenuSelectHdl, Menu*, pMenu, bool)
     return false;
 }
 
+IMPL_STATIC_LINK_NOARG(SvxStyleBox_Impl, ShowMoreHdl, void*, void)
+{
+    SfxViewFrame* pViewFrm = SfxViewFrame::Current();
+    DBG_ASSERT( pViewFrm, "SvxStyleBox_Impl::Select(): no viewframe" );
+    if (!pViewFrm)
+        return;
+    pViewFrm->ShowChildWindow(SID_SIDEBAR);
+    ::sfx2::sidebar::Sidebar::ShowPanel("StyleListPanel", pViewFrm->GetFrame().GetFrameInterface());
+}
+
 void SvxStyleBox_Impl::Select()
 {
     // Tell base class about selection so that AT get informed about it.
@@ -451,11 +462,7 @@ void SvxStyleBox_Impl::Select()
         }
         else if( aSearchEntry == aMoreKey && GetSelectedEntryPos() == ( GetEntryCount() - 1 ) )
         {
-            SfxViewFrame* pViewFrm = SfxViewFrame::Current();
-            DBG_ASSERT( pViewFrm, "SvxStyleBox_Impl::Select(): no viewframe" );
-            pViewFrm->ShowChildWindow( SID_SIDEBAR );
-            ::sfx2::sidebar::Sidebar::ShowPanel("StyleListPanel",
-                                                pViewFrm->GetFrame().GetFrameInterface());
+            Application::PostUserEvent(LINK(nullptr, SvxStyleBox_Impl, ShowMoreHdl));
             //tdf#113214 change text back to previous entry
             SetText(GetSavedValue());
             bDoIt = false;