Don't start setting until the initial get succeeds

Divorce selecting the appropriate broker with subscribing to that broker, they
have to be separate actions.

Thanks to Aaron Kavlie for finding the bug.

offset_manager.go

@@ -168,6 +168,8 @@ func (om *offsetManager) newPartitionOffsetManager(topic string, partition int32
 		return nil, err
 	}
 
+	pom.broker.updateSubscriptions <- pom
+
 	go withRecover(pom.mainLoop)
 
 	return pom, nil
@@ -180,6 +182,8 @@ func (pom *partitionOffsetManager) mainLoop() {
 			if err := pom.selectBroker(); err != nil {
 				pom.handleError(err)
 				pom.rebalance <- none{}
+			} else {
+				pom.broker.updateSubscriptions <- pom
 			}
 		case <-pom.dying:
 			if pom.broker != nil {
@@ -213,7 +217,6 @@ func (pom *partitionOffsetManager) selectBroker() error {
 	}
 
 	pom.broker = pom.parent.refBrokerOffsetManager(broker)
-	pom.broker.updateSubscriptions <- pom
 	return nil
 }
 
@@ -362,7 +365,9 @@ func (bom *brokerOffsetManager) mainLoop() {
 	for {
 		select {
 		case <-bom.timer.C:
-			bom.flushToBroker()
+			if len(bom.subscriptions) > 0 {
+				bom.flushToBroker()
+			}
 		case s, ok := <-bom.updateSubscriptions:
 			if !ok {
 				bom.timer.Stop()