treat the string passed to MakeRelativeTo() as directory even if it doesn't have a trailing slash

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@22059 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/filename.cpp

@@ -998,7 +998,7 @@ bool wxFileName::IsAbsolute(wxPathFormat format) const
 
 bool wxFileName::MakeRelativeTo(const wxString& pathBase, wxPathFormat format)
 {
-    wxFileName fnBase(pathBase, format);
+    wxFileName fnBase = wxFileName::DirName(pathBase, format);
 
     // get cwd only once - small time saving
     wxString cwd = wxGetCwd();