Always use UTF-8 for GTK+ strings.

Strings returned and accepted by GTK+ functions always use UTF-8 independently
of the current locale and of the file name encoding we use. So use UTF-8
instead of wxConvFileName everywhere where we deal with GTK+ directly.

Closes #11743.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63549 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/filedlg.cpp

@@ -51,7 +51,7 @@ static void gtk_filedialog_ok_callback(GtkWidget *widget, wxFileDialog *dialog)
 
                 msg.Printf(
                     _("File '%s' already exists, do you really want to overwrite it?"),
-                    wxString(filename, *wxConvFileName));
+                    wxString::FromUTF8(filename));
 
                 wxMessageDialog dlg(dialog, msg, _("Confirm"),
                                    wxYES_NO | wxICON_QUESTION);