Citadel Search: Wrong counts in sidebar when searching in categories

To reproduce: Going into [this search](https://indico.cern.ch/category/11136/search?q=cooling) and clicking on any of the sidebar filters which report to have a high count of entries. CERN, the first one in Affiliations shows 15k and has 0 results.

Start by reproducing the linked Citadel Search query for “cooling” in category 11136, then click the sidebar affiliation filters, beginning with CERN. Trace the search and sidebar-count entry points from there; done means each displayed count corresponds to the results returned by its filter, rather than showing a large count with zero results.

Written by the indexing model from the issue text.