Extract layergroup data augmentation to its own "middleware"

lib/cartodb/controllers/map.js

@@ -332,11 +332,6 @@ MapController.prototype.afterLayergroupCreate = function (req, res, callback) {
         }
     };
 
-    // include in layergroup response the variables in serverMedata
-    // those variables are useful to send to the client information
-    // about how to reach this server or information about it
-    _.extend(layergroup, global.environment.serverMetadata);
-
     // Don't wait for the mapview count increment to
     // take place before proceeding. Error will be logged
     // asynchronously
@@ -349,7 +344,11 @@ MapController.prototype.afterLayergroupCreate = function (req, res, callback) {
     });
 
     step(
-        function getAffectedTables () {
+        function () {
+            self.augmentLayergroupData(req, res, this);
+        },
+        function getAffectedTables (err) {
+            assert.ifError(err);
             self.getAffectedTables(req, res, this);
         },
         function setCacheChannel (err) {
@@ -374,6 +373,17 @@ MapController.prototype.afterLayergroupCreate = function (req, res, callback) {
     );
 };
 
+MapController.prototype.augmentLayergroupData = function (req, res, callback) {
+    const { layergroup } = res.locals;
+
+    // include in layergroup response the variables in serverMedata
+    // those variables are useful to send to the client information
+    // about how to reach this server or information about it
+    _.extend(layergroup, global.environment.serverMetadata);
+
+    callback();
+}
+
 MapController.prototype.getAffectedTables = function (req, res, callback) {
     const self = this;
     const { dbname, layergroup, user, mapconfig } = res.locals;