Add a fall back for when the thumbnail is not generated for a task

Re-add scrim and shadows to cards.

This can happen on TV when an App is mid launch and the HOME button
is pressed. The Banner of the App is used as a fallback, with the
icon of the app as a final fallback. The icon should not be used
normally, since an App would fail review for not providing a banner.

BUG: 27349208
BUG: 27857124
BUG: 27953609
Change-Id: I50f6ee714eeddee1ea2b5ae31f23ea68d230bc59