Zooming via clustered Features is rather erratic

[lonvia]

I think we need to do something about zooming in when clicking on clusters. I get really odd behaviour at times. Sometimes it zooms out instead of in, sometiles it doesn't zoom at all.

Example of not zooming at all: https://nominatim.org/qa/#map=10.00/35.32/139.91&layer=same_wikidata (try clicking on the large 3-digit number, "172" as of today)

I can't provide an example where it zooms out. I think what happens is that there is a place where there is no tile at the current zoom level, so the cluster item of a lower zoom level is shown instead.