Need to update the bg brush when the first page is added.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41642 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/notebook.cpp

@@ -761,6 +761,13 @@ bool wxNotebook::InsertPage(size_t nPage,
         return false;
     }
 
+    // need to update the bg brush when the first page is added
+    // so the first panel gets the correct themed background
+    if ( m_pages.empty() )
+    {
+        UpdateBgBrush();
+    }
+
     // succeeded: save the pointer to the page
     m_pages.Insert(pPage, nPage);