call cb even if email service is not defined

lib/blockchainmonitor.js

@@ -133,9 +133,9 @@ BlockchainMonitor.prototype._createNotification = function(walletId, txid, addre
   self.storage.storeNotification(walletId, notification, function() {
     self.messageBroker.send(notification)
     if (self.emailService) {
-      self.emailService.sendEmail(notification, function() {
-        if (cb) return cb();
-      });
+      self.emailService.sendEmail(notification, cb);
+    } else {
+      return cb();
     }
   });
 };