Coverity - Accesing attribute of null

There is a possibility that widget is null and then there could be an error.
Therefore there is new check of widget variable.

Reviewed-By: Petr Vobornik <pvoborni@redhat.com>

install/ui/src/freeipa/widgets/APIBrowserWidget.js

@@ -252,7 +252,7 @@ widgets.APIBrowserWidget = declare([Stateful, Evented], {
         }
 
         // switch widget
-        if (!widget.el) widget.render();
+        if (widget && !widget.el) widget.render();
         if (this.current_details_w !== widget) {
             this.details_el.empty();
             this.details_el.append(widget.el);