fix(notify): Fixed race condition in listener. (#1963)
fix(notify): Fixed race condition in listener. (#1963)

This resolves a race condition in listener where `ln.closed` was being
read without a mutex at the same time it could be written. Just move the
mutex unlock for `Unlisten` down, **but not defer it** so that the mutex
still holds the lock properly. But does not cause a deadlock with
release conn.
go-pg/pg,go-pg/pg