Fixed gateway flapper
Fixed gateway flapper

Need to make sure message is received before unsub'ing because
otherwise it would be possible that the unsub happens before
message is delivered, which would have resulted in an RS- while
we were expecting the message to not cause one.

Signed-off-by: Ivan Kozlovic <a15f8b81a160b4eebe5c84e9e3b65c87b9b2f18e@synadia.com>

apcera/gnatsd,nats-io/gnatsd,wallyqs/gnatsd,apcera/gnatsd,nats-io/gnatsd,wallyqs/gnatsd