Bug 1024333 - [v1.4][UX]Cannot turn off recent app page by tapping screen when "No recent app" is display

* Check if the cardsView is empty and should be closed or not in the onStartEvent event handler.
* Add test for closing empty cardsview by touchstart.
Merge pull request #21427 from begeeben/1024333_no_recent_app

Bug 1024333 - [v1.4][UX]Cannot turn off recent app page by tapping screen when "No recent app" is display, r=alive