[FIX] web_kanban: position of kanban_no_content

In sales dashboard, when there is no sales team, the no content message is displayed next to the dashboard.
The class o_kanban_ungrouped adds style to avoid this problem.

Credits to @qsm-odoo.

addons/web_kanban/static/src/js/kanban_view.js

@@ -364,6 +364,7 @@ var KanbanView = View.extend({
             this.$el.addClass('o_kanban_grouped');
             this.render_grouped(fragment);
         } else if (this.data.is_empty) {
+            this.$el.addClass('o_kanban_ungrouped');
             this.render_no_content(fragment);
         } else {
             this.$el.addClass('o_kanban_ungrouped');