pubsub: Report a non-nil error when shutting down. #7309
Merged
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If a subscriber arrives while the pubsub service is shutting down, the existing
code will return a nil subscription without error. With unlucky timing, this
may lead to a nil indirection panic in the RPC service.
To avoid that problem, make sure that when a subscription fails for this
reason, we report a non-nil error so that the client will detect it and give up
gracefully.
Fixes #7306.