SetSelection(wxNOT_FOUND) now works correctly.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42081 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/univ/listbox.cpp

@@ -483,6 +483,7 @@ void wxListBox::DoSetSelection(int n, bool select)
                 // selecting an item in a single selection listbox deselects
                 // all the others
                 DeselectAll();
+                return;
             }
 
             m_selections.Add(n);