Make UI refresh when there is only one contextual card left.

After having card dismissal mechanism implemented, it is possible that
the card list loaded from the card loader will be empty (users may
dismiss all cards). When there is only one card remaining on the screen
and user dismiss it, the card should go away.

Fixes: 119580732
Test: robotest
Change-Id: I7ae3b03f16a0b8b009d8aa77811b5a6d39c359e7