Update a Slice Uri when unavailable

When a slice becomes unavailable, it should not update the
underlying data even if the view has not changed.

When we receive a change from an unavailable slice, notifychange
on the Uri and do not change the underlying data.

Change-Id: I91851ab668e4aece669fd65c14e0dc4ec2edefdf
Fixes: 77980406
Test: robotests