Split from T129366: List wikis and pages with unread notifications in the Notification Page left nav

If there are no unread notifications in any wiki, the current wiki will still be shown.

According to specs, even if there are 0 notifications in the current wiki (read and unread), the current wiki should be shown.
But instead, 'No notificaitons' will be displayed on Special:Notifications.

Steps to reproduce (referring to the user in the screenshots below):

1. User ET94 was created in zhwiki.
2. ET94 goes to enwiki Special:Notifications and sees 'No notifications' displayed because in enwiki the user does not have any notifications.