[FIX] web: fix dataset to avoid race conditions

The read_slice method in dataset is problematic, because it alters the
dataset ids.  So, if 2 consecutive read_slice are started, but the first
one ends after the second one, we don't have the correct ids in the
dataset.

This commit just make sure that previous read_slice do not alter the ids
of the next read_slice.

addons/web/static/src/js/framework/data.js

@@ -320,6 +320,7 @@ var DataSet =  Class.extend(mixins.PropertiesMixin, {
         this.index = null;
         this._sort = [];
         this._model = new Model(model, context);
+        this.orderer = new utils.DropMisordered();
     },
     previous: function () {
         this.index -= 1;
@@ -408,10 +409,11 @@ var DataSet =  Class.extend(mixins.PropertiesMixin, {
     read_slice: function (fields, options) {
         var self = this;
         options = options || {};
-        return this._model.query(fields)
+        var query = this._model.query(fields)
                 .limit(options.limit || false)
                 .offset(options.offset || 0)
-                .all().done(function (records) {
+                .all();
+        return this.orderer.add(query).done(function (records) {
             self.ids = _(records).pluck('id');
         });
     },