ensure that dialog gripper is always positioned below the other children, even if they're created after it (#9519)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@54009 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/dialog.h

@@ -116,6 +116,11 @@ protected:
     void ResizeGripper();
 
 private:
+    // this function is used to adjust Z-order of new children relative to the
+    // gripper if we have one
+    void OnWindowCreate(wxWindowCreateEvent& event);
+
+
     wxWindow*   m_oldFocus;
     bool        m_endModalCalled; // allow for closing within InitDialog