luci-base: cbi.js: handle ui elements which return a promise in render()

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

modules/luci-base/htdocs/luci-static/resources/cbi.js

@@ -321,9 +321,11 @@ function cbi_init() {
 		    widget = new (Function.prototype.bind.apply(L.ui[args[0]], args)),
 		    markup = widget.render();
 
+		Promise.resolve(markup).then(function(markup) {
 			markup.addEventListener('widget-change', cbi_d_update);
 			node.parentNode.replaceChild(markup, node);
 		});
+	});
 
 	cbi_d_update();
 }