testappchooser: handle 'no app selected' gracefully

The test was assuming that it always gets an app info back,
when in reality it might get NULL back.

tests/testappchooser.c

@@ -41,11 +41,15 @@ dialog_response (GtkDialog *d,
   if (response_id == GTK_RESPONSE_OK)
     {
       app_info = gtk_app_chooser_get_app_info (GTK_APP_CHOOSER (d));
+      if (app_info)
+        {
           name = g_app_info_get_name (app_info);
           g_print ("Application selected: %s\n", name);
-
           g_object_unref (app_info);
         }
+      else
+        g_print ("No application selected\n");
+    }
 
   gtk_widget_destroy (GTK_WIDGET (d));
   dialog = NULL;