Made sure that the ambient single line view remains invisible

The single line views are visible by default when they are inflated
and not all calls to it actually ensure that the visibility is
updated. We therefore make sure that the view is appropriately
hidden.

Change-Id: Ied7641347d910fff5c8f1f0b38d349e7f3b56b76
Fixes: 77290485
Test: add second notification to group, observe no overlapping text