[Font Inspector Plugin] Hide "Add Feature" button if supported feature list is empty.

editor/import/dynamic_font_import_settings.cpp

@@ -1009,6 +1009,7 @@ void DynamicFontImportSettings::open_settings(const String &p_path) {
 
 	vars_list_root = vars_list->create_item();
 
+	import_settings_data->settings.clear();
 	import_settings_data->defaults.clear();
 	for (List<ResourceImporter::ImportOption>::Element *E = options_general.front(); E; E = E->next()) {
 		import_settings_data->defaults[E->get().option.name] = E->get().default_value;

editor/plugins/font_config_plugin.cpp

@@ -622,6 +622,16 @@ void EditorPropertyOTFeatures::update_property() {
 		supported = fd->get_supported_feature_list();
 	}
 
+	if (supported.is_empty()) {
+		edit->set_text(vformat(TTR("No supported features")));
+		if (container) {
+			set_bottom_editor(nullptr);
+			memdelete(container);
+			button_add = nullptr;
+			container = nullptr;
+		}
+		return;
+	}
 	edit->set_text(vformat(TTR("Features (%d of %d set)"), dict.size(), supported.size()));
 
 	bool unfolded = get_edited_object()->editor_is_section_unfolded(get_edited_property());