[FIX] hr: not set partner of a bank account to False

Steps to reproduce:
-------------------
- install `account` module;
- create an employee;
- add a bank account;
- add a related user and save;
- remove the user and save;

Issue:
------
A traceback occurs.

Cause:
------
We synchronize the `partner_id` of the `bank_account`
with the `work_contact_id`.
If the latter is `False`, this triggers an error.

Solution:
---------
Do not trigger the logic that updates the `partner_id` of
the `bank_account` if the value is `False`.
This keeps the logic that the `partner_id` field
in the `res.partner.bank` model is required.

opw-3558983

closes odoo/odoo#139570

X-original-commit: c19574e26d8814a745152489eb16915f13b2a6c0
Signed-off-by: Sofie Gvaladze (sgv) <sgv@odoo.com>
Signed-off-by: Thomas Lefebvre (thle) <thle@odoo.com>

addons/hr/models/hr_employee.py

@@ -415,7 +415,8 @@ class HrEmployeePrivate(models.Model):
                     if vals['work_contact_id'] != bank_account.partner_id.id:
                         if bank_account.allow_out_payment:
                             bank_account.sudo().allow_out_payment = False
-                        bank_account.partner_id = vals['work_contact_id']
+                        if vals['work_contact_id']:
+                            bank_account.partner_id = vals['work_contact_id']
             self.message_unsubscribe(self.work_contact_id.ids)
             if vals['work_contact_id']:
                 self._message_subscribe([vals['work_contact_id']])