Escape FLTK menu entries

We don't want it automatically creating submenus when least
expected.
diff --git a/vncviewer/OptionsDialog.cxx b/vncviewer/OptionsDialog.cxx
index b9752aa..9fa9a66 100644
--- a/vncviewer/OptionsDialog.cxx
+++ b/vncviewer/OptionsDialog.cxx
@@ -724,9 +724,9 @@
 
   menuKeyChoice = new Fl_Choice(LBLLEFT(tx, ty, 150, CHOICE_HEIGHT, _("Menu key")));
 
-  menuKeyChoice->add(_("None"), 0, NULL, (void*)0, FL_MENU_DIVIDER);
+  fltk_menu_add(menuKeyChoice, _("None"), 0, NULL, (void*)0, FL_MENU_DIVIDER);
   for (int i = 0; i < getMenuKeySymbolCount(); i++)
-    menuKeyChoice->add(getMenuKeySymbols()[i].name, 0, NULL, 0, 0);
+    fltk_menu_add(menuKeyChoice, getMenuKeySymbols()[i].name, 0, NULL, 0, 0);
 
   ty += CHOICE_HEIGHT + TIGHT_MARGIN;