Test SEPA mandate sequence of the company of the mandate instead of the context

Closes #13882
(grafted from fd065f036503c116574e45bccd836b240d248a02)

--HG--
branch : 6.0

modules/account_payment_sepa/payment.py

@@ -596,11 +596,12 @@ class Mandate(Workflow, ModelSQL, ModelView):
         vlist = [v.copy() for v in vlist]
         default_company = cls.default_company()
         for values in vlist:
-            if (config.sepa_mandate_sequence
-                    and not values.get('identification')):
-                values['identification'] = config.get_multivalue(
+            if not values.get('identification'):
+                sequence = config.get_multivalue(
                     'sepa_mandate_sequence',
-                    company=values.get('company', default_company)).get()
+                    company=values.get('company', default_company))
+                if sequence:
+                    values['identification'] = sequence.get()
             # Prevent raising false unique constraint
             if values.get('identification') == '':
                 values['identification'] = None