[FIX] Contract to Invoice: take contract vendor instead of partner's

contract/models/contract.py

@@ -253,7 +253,7 @@ class AccountAnalyticAccount(models.Model):
             'journal_id': journal.id,
             'origin': self.name,
             'company_id': self.company_id.id,
-            'user_id': self.partner_id.user_id.id,
+            'user_id': self.user_id.id,
             'payment_term_id': self.payment_term_id.id,
             'fiscal_position_id': self.fiscal_position_id.id,
         }

contract/tests/test_contract.py

@@ -154,7 +154,7 @@ class TestContract(TestContractBase):
         self.assertTrue(self.inv_line.invoice_line_tax_ids)
         self.assertAlmostEqual(self.inv_line.price_subtotal, 50.0)
         self.assertEqual(
-            self.contract.partner_id.user_id, self.invoice_monthly.user_id
+            self.contract.user_id, self.invoice_monthly.user_id
         )
 
     def test_contract_recurring_next_date(self):