don't reset the selection after event was vetoed if there is no old selection

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@40805 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/treebkg.cpp

@@ -651,7 +651,8 @@ int wxTreebook::DoSetSelection(size_t pagePos)
     else // page change vetoed
     {
         // tree selection might have already had changed
-        tree->SelectItem(DoInternalGetPage(oldSel));
+        if ( oldSel != wxNOT_FOUND )
+            tree->SelectItem(DoInternalGetPage(oldSel));
     }
 
     return oldSel;