Fix typo in for loop over select_list

src/jio.storage/mappingstorage.js

@@ -515,7 +515,7 @@
       }
     }
     if (this._query.select_list !== undefined) {
-      for (i = 0; i < this._query.select_list; i += 1) {
+      for (i = 0; i < this._query.select_list.length; i += 1) {
         property = this._query.select_list[i];
         if (select_list.indexOf(property) < 0) {
           select_list.push(property);