Merge pull request #3477 from nats-io/js_fix_panic_on_peer_remove

[FIXED] JetStream: possible panic on peer remove on server shutdown

server/jetstream_cluster.go

@@ -1299,6 +1299,10 @@ func (js *jetStream) processAddPeer(peer string) {
 func (js *jetStream) processRemovePeer(peer string) {
 	js.mu.Lock()
 	s, cc := js.srv, js.cluster
+	if cc.meta == nil {
+		js.mu.Unlock()
+		return
+	}
 	isLeader := cc.isLeader()
 	// All nodes will check if this is them.
 	isUs := cc.meta.ID() == peer