[FIX] save wizard before run

we must save 'account.invoice.line.update' to be able match them to real invoice lines,

account_invoice_update_wizard/models/account_invoice.py

@@ -0,0 +1,22 @@
+# Copyright 2019 Camptocamp
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+from odoo import models, fields, api, _
+from odoo.exceptions import UserError
+import odoo.addons.decimal_precision as dp
+
+
+class AccountInvoice(models.Model):
+    _inherit = 'account.invoice'
+    
+    def prepare_update_wizard(self):
+        self.ensure_one()
+        wizard = self.env['account.invoice.update']
+        res = wizard._prepare_default_get(self)
+        action = self.env.ref(
+            'account_invoice_update_wizard.account_invoice_update_action'
+        ).read()[0]
+        action['name'] = "Update Wizard"
+        action['res_id'] = wizard.create(res).id
+        return action
+