See if we want to add the checks in https://github.com/openshift/prometheus/pull/227 (last commits) to thanos ruler and querier.

Queries with broken selectors may be sent to thanos querier without necessarily reaching the checks added into Prometheus (no alert on prometheus would be triggered)

Thanos ruler may be evaluating rules with broken selectors.

The check will consists of adding the same code into the Prometheus parser that Thanos imports.