[FIX] point_of_sale: prevent deletion of POS bank statement

Nothing prevents to delete a bank statement linked to an open pos session,
which leads to a KeyError when validating and posting entries at closure.

closes odoo/odoo#44229

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

addons/point_of_sale/i18n/point_of_sale.pot

@@ -5044,6 +5044,12 @@ msgstr ""
 msgid "You cannot create a session before the accounting lock date."
 msgstr ""
 
+#. module: point_of_sale
+#: code:addons/point_of_sale/models/account_bank_statement.py:0
+#, python-format
+msgid "You cannot delete a bank statement used in an open Point of Sale session."
+msgstr ""
+
 #. module: point_of_sale
 #: code:addons/point_of_sale/models/product.py:0
 #: code:addons/point_of_sale/models/product.py:0

addons/point_of_sale/models/account_bank_statement.py

@@ -17,6 +17,11 @@ class AccountBankStatement(models.Model):
                 raise UserError(_("You can't validate a bank statement that is used in an opened Session of a Point of Sale."))
         return super( AccountBankStatement, self).check_confirm_bank()
 
+    def unlink(self):
+        for bs in self:
+            if bs.pos_session_id:
+                raise UserError(_("You cannot delete a bank statement used in an open Point of Sale session."))
+        return super( AccountBankStatement, self).unlink()
 
 class AccountBankStatementLine(models.Model):
     _inherit = 'account.bank.statement.line'