fix Unicode build after last change (closes #10649)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@59909 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/filename.cpp

@@ -2143,7 +2143,7 @@ void wxFileName::SplitPath(const wxString& fullpath,
 wxString wxFileName::StripExtension(const wxString& fullpath)
 {
     wxFileName fn(fullpath);
-    fn.SetExt("");
+    fn.SetExt(_T(""));
     return fn.GetFullPath();
 }