Bug Fix: Skip Elasticsearch index / database count comparison health check if no index exists

In a multisite context, if one site has VIP Search all sites have access to VIP Search. Even if they don’t have an index. This is problematic as it logs false positives in our health checks. To prevent this from happening, we now skip site / indexable combos that don’t exist.

https://github.com/Automattic/vip-go-mu-plugins/pull/1933