server: fix race

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

server/noop.go

@@ -281,14 +281,15 @@ func (n *noopServer) Deregister() error {
 			if sb.Options().Context != nil {
 				cx = sb.Options().Context
 			}
-
+			
+			ncx := cx
 			wg.Add(1)
 			go func(s broker.Subscriber) {
 				defer wg.Done()
 				if config.Logger.V(logger.InfoLevel) {
 					config.Logger.Infof(n.opts.Context, "unsubscribing from topic: %s", s.Topic())
 				}
-				if err := s.Unsubscribe(cx); err != nil {
+				if err := s.Unsubscribe(ncx); err != nil {
 					if config.Logger.V(logger.ErrorLevel) {
 						config.Logger.Errorf(n.opts.Context, "unsubscribing from topic: %s err: %v", s.Topic(), err)
 					}

server/server.go

@@ -11,7 +11,7 @@ import (
 )
 
 // DefaultServer default server
-var DefaultServer Server = NewServer()
+var DefaultServer = NewServer()
 
 var (
 	// DefaultAddress will be used if no address passed, use secure localhost