[util] Fix leak of an hb_font_t

util/font-options.hh

@@ -83,6 +83,7 @@ static struct supported_font_funcs_t {
 void
 font_options_t::post_parse (GError **error)
 {
+  assert (!font);
   font = hb_font_create (face);
 
   if (font_size_x == FONT_SIZE_UPEM)
@@ -272,7 +273,8 @@ font_options_t::add_options (option_parser_t *parser)
 		     "font",
 		     "Font-instance options:",
 		     "Options for the font instance",
-		     this);
+		     this,
+		     false /* We add below. */);
 
   const gchar *variations_help = "Comma-separated list of font variations\n"
     "\n"

util/options.hh

@@ -110,11 +110,13 @@ struct option_parser_t
 		  const gchar    *name,
 		  const gchar    *description,
 		  const gchar    *help_description,
-		  Type           *closure)
+		  Type           *closure,
+		  bool		  add_parse_hooks = true)
   {
     GOptionGroup *group = g_option_group_new (name, description, help_description,
 					      static_cast<gpointer>(closure), nullptr);
     g_option_group_add_entries (group, entries);
+    if (add_parse_hooks)
       g_option_group_set_parse_hooks (group, nullptr, post_parse<Type>);
     g_option_context_add_group (context, group);
   }