[FIX] web_kanban: reference for loaded more records

If the kanban view is loading grouped records, the dataset of the view
itself is the concatenation of the dataset of each groups.

But when using "Load  more..." on a column, these records are not added
in the view dataset which is thus desynchronised. This could lead to an
error down the road.

closes #10156
opw-659016

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

@@ -706,6 +706,7 @@ var KanbanView = View.extend({
         return this.load_records(offset, column.dataset).then(function (result) {
             _.each(result.records, function (r) {
                 column.add_record(r, {no_update: true});
+                self.dataset.add_ids([r.id]);
             });
             column.offset += self.limit;
             column.remaining = Math.max(column.remaining - self.limit, 0);