[FIX] point_of_sale: unable to close open session with deleted journal

Steps to reproduce the bug:
- Create POS (P)
- Create journal (J) and link it to (P)
- Open a new session in (P)
- Exit the session without closing it
- Delete (J)

Bug:
You cannot close the session nor assign a new journal to the POS.

opw:2347169

closes odoo/odoo#59097

X-original-commit: 636f1358e72e65a3210c95c60d1703c9cbd914dc
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>
Signed-off-by: backspac <backspac@users.noreply.github.com>

addons/point_of_sale/models/pos_config.py

@@ -111,7 +111,8 @@ class PosConfig(models.Model):
         'account.journal', string='Sales Journal',
         domain=[('type', '=', 'sale')],
         help="Accounting journal used to post sales entries.",
-        default=_default_sale_journal)
+        default=_default_sale_journal,
+        ondelete='restrict')
     invoice_journal_id = fields.Many2one(
         'account.journal', string='Invoice Journal',
         domain=[('type', '=', 'sale')],

addons/point_of_sale/models/pos_order.py

@@ -246,7 +246,7 @@ class PosOrder(models.Model):
     note = fields.Text(string='Internal Notes')
     nb_print = fields.Integer(string='Number of Print', readonly=True, copy=False, default=0)
     pos_reference = fields.Char(string='Receipt Number', readonly=True, copy=False)
-    sale_journal = fields.Many2one('account.journal', related='session_id.config_id.journal_id', string='Sales Journal', store=True, readonly=True)
+    sale_journal = fields.Many2one('account.journal', related='session_id.config_id.journal_id', string='Sales Journal', store=True, readonly=True, ondelete='restrict')
     fiscal_position_id = fields.Many2one(
         comodel_name='account.fiscal.position', string='Fiscal Position',
         readonly=True,