[FIX] hr_employee: ensure desynchronization with user

Steps to reproduce:
-------------------
- create a new employee;
- link it to an existing user;
- save (trigger a validation error);
- remove the related user;
- save;
- change the email address of this new employee;

Issue:
------
The email address of the employee linked to the user
that we tried to link is updated.

Cause:
------
We don't sync the employee with the user if the user is `False`,
i.e. we don't update the employee's `work_contact_id` if the `user_id` is `False`.

Solution:
---------
Update the `work_contact_id` in any case.

opw-3475002

closes odoo/odoo#133191

X-original-commit: c2f2dc3e49ee7cd96d4da05f2236441e65090753
Signed-off-by: Sofie Gvaladze (sgv) <sgv@odoo.com>
Signed-off-by: Thomas Lefebvre (thle) <thle@odoo.com>

addons/hr/models/hr_employee.py

@@ -332,10 +332,9 @@ class HrEmployeePrivate(models.Model):
 
     @api.onchange('user_id')
     def _onchange_user(self):
-        if self.user_id:
-            self.update(self._sync_user(self.user_id, (bool(self.image_1920))))
-            if not self.name:
-                self.name = self.user_id.name
+        self.update(self._sync_user(self.user_id, (bool(self.image_1920))))
+        if not self.name:
+            self.name = self.user_id.name
 
     @api.onchange('resource_calendar_id')
     def _onchange_timezone(self):