[FIX] project: fix groupby by none issue in project sharing

Steps:
- Go to portal and select tasks and search anything in search bar.
- Showing  no tasks available
- choose group by none and search anything it will show table labels.

Fix:
shows warning when there is no record when groupby by none.

task-3183771

closes odoo/odoo#128560

X-original-commit: 1d858798f53d56e5b81cc9df0fa70113dedd4f50
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>

addons/project/controllers/portal.py

@@ -428,7 +428,7 @@ class ProjectCustomerPortal(CustomerPortal):
                 else:
                     grouped_tasks = [Task_sudo.concat(*g) for k, g in groupbyelem(tasks, itemgetter(group))]
             else:
-                grouped_tasks = [tasks]
+                grouped_tasks = [tasks] if tasks else []
 
 
             task_states = dict(Task_sudo._fields['state']._description_selection(request.env))