[FIX] web: Kanban: fallback on empty array for x2many raw_value

The commit e07f27d has wrongly changed the fallback for one2many raw_value from
an empty array to `false`. This modification brokes a lot of templates where we
assume that the value is always an array.

This commit restores the previous behavior with the fallback on [].

addons/web/static/src/js/views/kanban/kanban_record.js

@@ -368,7 +368,7 @@ var KanbanRecord = Widget.extend({
             if ((r.type === 'date' || r.type === 'datetime') && value) {
                 r.raw_value = value.toDate();
             } else if (r.type === 'one2many' || r.type === 'many2many') {
-                r.raw_value = value.count ? value.res_ids : false;
+                r.raw_value = value.count ? value.res_ids : [];
             } else if (r.type === 'many2one' ) {
                 r.raw_value = value && value.res_id || false;
             } else {

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

@@ -1031,7 +1031,7 @@ QUnit.module('Views', {
                     '<templates><t t-name="kanban-box">' +
                         '<div>' +
                         '<button t-if="!record.product_id.raw_value" class="btn_a">A</button>' +
-                        '<button t-if="!record.category_ids.raw_value" class="btn_b">B</button>' +
+                        '<button t-if="!record.category_ids.raw_value.length" class="btn_b">B</button>' +
                         '</div>' +
                     '</t></templates>' +
                 '</kanban>',