Fix race

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

server/consumer.go

@@ -322,6 +322,15 @@ func (mset *Stream) AddConsumer(config *ConsumerConfig) (*Consumer, error) {
 		}
 	}
 
+	// Grab the client, account and server reference.
+	c := mset.client
+	if c == nil {
+		return nil, fmt.Errorf("stream not valid")
+	}
+	c.mu.Lock()
+	s, a := c.srv, c.acc
+	c.mu.Unlock()
+
 	// Hold mset lock here.
 	mset.mu.Lock()
 
@@ -387,6 +396,7 @@ func (mset *Stream) AddConsumer(config *ConsumerConfig) (*Consumer, error) {
 	// Set name, which will be durable name if set, otherwise we create one at random.
 	o := &Consumer{
 		mset:    mset,
+		acc:     a,
 		config:  *config,
 		dsubj:   config.DeliverSubject,
 		active:  true,
@@ -459,14 +469,6 @@ func (mset *Stream) AddConsumer(config *ConsumerConfig) (*Consumer, error) {
 	o.selectStartingSeqNo()
 
 	// Now register with mset and create the ack subscription.
-	c := mset.client
-	if c == nil {
-		mset.mu.Unlock()
-		return nil, fmt.Errorf("stream not valid")
-	}
-	s, a := c.srv, c.acc
-	o.acc = a
-
 	// Check if we already have this one registered.
 	if eo, ok := mset.consumers[o.name]; ok {
 		mset.mu.Unlock()