scroll capture: Recover gracefully when anchor view is lost

When manipulating a RecyclerView, the position of a visible child
view is used as a feedback signal for scroll tracking. If the view
remains detached after scrolling, view operations fail and crash
the application.

Detect this condition and return an empty result. If the RecyclerView
moved during this request, the remaining tiles will be offset by the
same amount. This will manifest as a missing section of content.

Logging has been added to identify and track this bug.

Test: manual repro w/test app; see bug
Bug: 239050369
Change-Id: I5a0a62aaad10ffa7838d7902fd9c5f4f84b52ce6