Use turbocarto only if there's a layer

Author: Rafa de la Torre

lib/torque/renderer/point.js

@@ -123,7 +123,7 @@ var CartoDatasource = require('./datasource');
 
       this.style = stripComments(cartocss);
 
-      if (PointRenderer.isTurboCarto(this.style)) {
+      if (PointRenderer.isTurboCarto(this.style) && self.layer) {
         var datasource = new CartoDatasource(self.layer._tiles);
         turbocarto(this.style, datasource, function (err, parsedCartoCSS) {
           if (err) {