[IMP] account_payment_partner: Fill payment mode in invoices if none is provided

Using same method as in upstream, payment mode is filled on invoice creation if
no payment method is provided. This way, we don't need to install
account_payment_sale if we don't want to handle several payment modes at sales
level. Even more, if we install the module later and we have already existing
sales orders without payment mode filled, those orders will be invoiced with
the customer payment mode.

account_payment_partner/__openerp__.py

@@ -5,7 +5,7 @@
 
 {
     'name': 'Account Payment Partner',
-    'version': '9.0.1.0.0',
+    'version': '9.0.1.1.0',
     'category': 'Banking addons',
     'license': 'AGPL-3',
     'summary': 'Adds payment mode on partners and invoices',

account_payment_partner/models/account_invoice.py

@@ -19,7 +19,7 @@ class AccountInvoice(models.Model):
 
     @api.onchange('partner_id', 'company_id')
     def _onchange_partner_id(self):
-        super(AccountInvoice, self)._onchange_partner_id()
+        res = super(AccountInvoice, self)._onchange_partner_id()
         if self.partner_id:
             if self.type == 'in_invoice':
                 pay_mode = self.partner_id.supplier_payment_mode_id
@@ -41,6 +41,25 @@ class AccountInvoice(models.Model):
             self.payment_mode_id = False
             if self.type == 'in_invoice':
                 self.partner_bank_id = False
+        return res
+
+    @api.model
+    def create(self, vals):
+        """Fill the payment_mode_id from the partner if none is provided on
+        creation, using same method as upstream."""
+        onchanges = {
+            '_onchange_partner_id': ['payment_mode_id'],
+        }
+        for onchange_method, changed_fields in onchanges.items():
+            if any(f not in vals for f in changed_fields):
+                invoice = self.new(vals)
+                getattr(invoice, onchange_method)()
+                for field in changed_fields:
+                    if field not in vals and invoice[field]:
+                        vals[field] = invoice._fields[field].convert_to_write(
+                            invoice[field],
+                        )
+        return super(AccountInvoice, self).create(vals)
 
     @api.onchange('payment_mode_id')
     def payment_mode_id_change(self):