Restrict the tests added in r70987 to run when using UTF-8 strings only, they test for something that is simply not true (and for a bug that can't happen) with non-multibyte encodings. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71384 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775