invalidate bg brush in the beginning of OnSize() to avoid using outdated brush for child pages background painting

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31275 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/notebook.cpp

@@ -679,6 +679,10 @@ int wxNotebook::HitTest(const wxPoint& pt, long *flags) const
 
 void wxNotebook::OnSize(wxSizeEvent& event)
 {
+#if wxUSE_UXTHEME
+  UpdateBgBrush();
+#endif // wxUSE_UXTHEME
+
   // fit the notebook page to the tab control's display area
   RECT rc;
   rc.left = rc.top = 0;
@@ -717,10 +721,6 @@ void wxNotebook::OnSize(wxSizeEvent& event)
     pPage->SetSize(rc.left, rc.top, width, height);
   }
 
-#if wxUSE_UXTHEME
-  UpdateBgBrush();
-#endif // wxUSE_UXTHEME
-
   event.Skip();
 }