Don't use time.After if there is no timeout

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

pkg/pubsub/publisher.go

@@ -58,10 +58,17 @@ func (p *Publisher) Publish(v interface{}) {
 	p.m.RLock()
 	for sub := range p.subscribers {
 		// send under a select as to not block if the receiver is unavailable
+		if p.timeout > 0 {
 			select {
 			case sub <- v:
 			case <-time.After(p.timeout):
 			}
+			continue
+		}
+		select {
+		case sub <- v:
+		default:
+		}
 	}
 	p.m.RUnlock()
 }