[FIX] web: graph: reload with correct fields

A traceback occurred when trying to reload a graph view with no
groupBy in the searchview, because the array of fields to read
given to the read_group RPC didn't contain the default groupBy
field (Error "Fields in 'groupby' must appear in the list of
fields to read"), e.g. in Sales > My Pipeline.

addons/web/static/src/js/views/graph/graph_model.js

@@ -114,13 +114,13 @@ return AbstractModel.extend({
      * @returns {Deferred}
      */
     _loadGraph: function () {
-        var fields = _.map(this.chart.groupedBy, function (groupBy) {
+        var groupedBy = this.chart.groupedBy.length ? this.chart.groupedBy : this.initialGroupBys;
+        var fields = _.map(groupedBy, function (groupBy) {
             return groupBy.split(':')[0];
         });
         if (this.chart.measure !== '__count__') {
             fields = fields.concat(this.chart.measure);
         }
-        var groupedBy = this.chart.groupedBy.length ? this.chart.groupedBy : this.initialGroupBys;
         return this._rpc({
                 model: this.modelName,
                 method: 'read_group',

addons/web/static/tests/views/graph_tests.js

@@ -372,6 +372,30 @@ QUnit.module('Views', {
         });
     });
 
+    QUnit.test('reload graph with correct fields', function (assert) {
+        assert.expect(2);
+
+        var graph = createView({
+            View: GraphView,
+            model: 'foo',
+            data: this.data,
+            arch: '<graph>' +
+                    '<field name="product_id" type="row"/>' +
+                    '<field name="foo" type="measure"/>' +
+                '</graph>',
+            mockRPC: function (route, args) {
+                if (args.method === 'read_group') {
+                    assert.deepEqual(args.kwargs.fields, ['product_id', 'foo'],
+                        "should read the correct fields");
+                }
+                return this._super.apply(this, arguments);
+            },
+        });
+
+        graph.reload({groupBy: []});
+
+        graph.destroy();
+    });
 });
 
 });