Automatic merge from submit-queue
prevent nil pointer when starting controllers before running the shar…
Fixes https://github.com/kubernetes/kubernetes/issues/25643.
https://github.com/kubernetes/kubernetes/pull/23795 changed initialization order, so the controller isn't guaranteed to be present at startup.
@mqliang @wojtek-t I'm pretty sure that we're not guaranteed to get back the correct `cache.Indexer` or `cache.Store` either. I'll look at re-plumbing the `AddIndexer` path to use the same instance so that its safe to use again.