Fix for API data race. (#4030)

Signed-off-by: Derek Collison <derek@nats.io>

server/events_test.go

@@ -1515,6 +1515,7 @@ func TestAccountClaimsUpdatesWithServiceImports(t *testing.T) {
 		nc.Publish(claimUpdateSubj, []byte(ajwt2))
 	}
 	nc.Flush()
+	time.Sleep(50 * time.Millisecond)
 
 	if startSubs < s.NumSubscriptions() {
 		t.Fatalf("Subscriptions leaked: %d vs %d", startSubs, s.NumSubscriptions())

server/jetstream_api.go

@@ -890,10 +890,17 @@ func (s *Server) sendAPIErrResponse(ci *ClientInfo, acc *Account, subject, reply
 const errRespDelay = 500 * time.Millisecond
 
 func (s *Server) sendDelayedAPIErrResponse(ci *ClientInfo, acc *Account, subject, reply, request, response string, rg *raftGroup) {
+	js := s.getJetStream()
+	if js == nil {
+		return
+	}
 	var quitCh <-chan struct{}
+	js.mu.RLock()
 	if rg != nil && rg.node != nil {
 		quitCh = rg.node.QuitC()
 	}
+	js.mu.RUnlock()
+
 	s.startGoRoutine(func() {
 		defer s.grWG.Done()
 		select {