Wrong facet counts with ISBN/ISSN query

[acka47]

Reported today via email by @frauhollunder.

bei wenigen Treffern sind die Filter zum Eingrenzen auf den
Gesamtbestand bezogen?

https://lobid.org/resources/search?id=0301-2999&name=&subject
https://lobid.org/resources/search?id=0301-2999&name=&subject=

Bei größeren Treffermengen sieht es gut aus:

https://lobid.org/resources/search?agent=&name=luhmann&subject
https://lobid.org/resources/search?agent=&name=luhmann&subject=

Screenshot:

[acka47]

The problem: The "ISBN/ISSN" query is a custom query, which in the background queries two fields (issn and isbn). When verbosely querying these fields the facet count is correct:

https://lobid.org/resources/search?q=issn%3A%220301-2999%22+OR+isbn%3A%220301-2999%22