[FIX] web: right labels in bar chart and comparison mode

For a single groupby selected, the graph view didn't render well
the data when simultaneously in bar chart and comparison mode.
The labels were in that case always integers.
This commit fixes that situation.

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

@@ -136,11 +136,7 @@ return AbstractRenderer.extend({
             }];
         } else if (this.state.groupedBy.length === 1) {
             values = this.state.data.map(function (datapt, index) {
-                if (self.state.comparisonData) {
-                    return {x: index, y: datapt.value};
-                } else {
-                    return {x: datapt.labels, y: datapt.value};
-                }
+                return {x: datapt.labels, y: datapt.value};
             });
             data.push({
                 values: values,
@@ -148,7 +144,7 @@ return AbstractRenderer.extend({
             });
             if (this.state.comparisonData) {
                 values = this.state.comparisonData.map(function (datapt, index) {
-                    return {x: index, y: datapt.value};
+                    return {x: datapt.labels, y: datapt.value};
                 });
                 data.push({
                     values: values,