Emit an error if a lookup in the ReadThroughCache doesn't fulfill any promise

A lookup of the ReadThroughCache should fulfill at least one promise. If that's not the case it means that there were some jumps back and forth in time.

A bit more of context: we have hit this problem a few times, the symptom is that a refresh hangs forever. We should think if we can throw an error or if this code should be an invariant.