[FIX] project: fix crash when no language selected

Reproduce the issue

    - Select a language (done by default)
    - Install Project
    - Create a project
    - Create a task with a formatted date
    - Reset the language
    - Go on the project

    Traceback

Cause

    In 7e42c663, I format the date_deadline based on the user's language
    but did'nt know that we could have no language selected.

This commit uses the `format_date` method from `odoo.tools.misc`
which fallback on the first language installed if there is no
language selected.

OPW-2146479

closes odoo/odoo#41037

Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/project/models/project.py

@@ -6,6 +6,7 @@ from datetime import timedelta
 from odoo import api, fields, models, tools, SUPERUSER_ID, _
 from odoo.exceptions import UserError, AccessError, ValidationError
 from odoo.tools.safe_eval import safe_eval
+from odoo.tools.misc import format_date
 
 
 class ProjectTaskType(models.Model):
@@ -544,9 +545,8 @@ class Task(models.Model):
 
     @api.depends('date_deadline')
     def _compute_date_deadline_formatted(self):
-        date_format = self.env['res.lang']._lang_get(self.env.user.lang).date_format
         for task in self:
-            task.date_deadline_formatted = task.date_deadline.strftime(date_format) if task.date_deadline else None
+            task.date_deadline_formatted = format_date(self.env, task.date_deadline) if task.date_deadline else None
 
     def _compute_attachment_ids(self):
         for task in self: