Only update the toolbar buttons if the toolbar is visible

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@52974 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/tbargtk.cpp

@@ -686,7 +686,7 @@ void wxToolBar::OnInternalIdle()
         }
     }
 
-    if (wxUpdateUIEvent::CanUpdate(this))
+    if (wxUpdateUIEvent::CanUpdate(this) && IsShownOnScreen())
         UpdateWindowUI(wxUPDATE_UI_FROMIDLE);
 }