ShuttlegGUI: const wxArrayStringEx & arguments, not wxArrayString *...

... for choice, combo, and listbox; reference allows passing temporaries,
eliminating need for some variables to hold the string arrays.

src/menus/TrackMenus.cpp

@@ -931,7 +931,7 @@ void OnResample(const CommandContext &context)
          {
             cb = S.AddCombo(_("New sample rate (Hz):"),
                             rate,
-                            &rates);
+                            rates);
          }
          S.EndHorizontalLay();