Check how filtering interacts with Room / index-key

[nikclayton]

Occasional reports (and experience) shows the position restoration code can still sometimes restore the user to the wrong place.

https://hostux.social/@olistan/113346824202033636 might be on to something. If posts are filtered and the filter is set to "Hide" the position in the timeline (measured as "count of visible posts") is going to be different to the position in the ordered database query that's used when restoring the position.