Restore instance context when getting account used

The account_used is set on property so it is executed under the transaction
context but we expect to have the account from the company set in the instance
context.

issue10557
review355371002
(grafted from bfeac28a3c0b44c48b9ad6ce560ade9e24b06789)

--HG--
branch : 6.0

product.py

@@ -4,6 +4,7 @@ from trytond.i18n import gettext
 from trytond.model import fields
 from trytond.pool import PoolMeta, Pool
 from trytond.pyson import Eval
+from trytond.transaction import Transaction
 
 from .exceptions import GiftCardValidationError
 
@@ -44,7 +45,10 @@ class Template(metaclass=PoolMeta):
         pool = Pool()
         Config = pool.get('account.configuration')
         if self.gift_card:
-            config = Config(1)
+            transaction = Transaction()
+            with transaction.reset_context(), \
+                    transaction.set_context(self._context):
+                config = Config(1)
             return config.gift_card_account_expense
         return super().account_expense_used
 
@@ -53,7 +57,10 @@ class Template(metaclass=PoolMeta):
         pool = Pool()
         Config = pool.get('account.configuration')
         if self.gift_card:
-            config = Config(1)
+            transaction = Transaction()
+            with transaction.reset_context(), \
+                    transaction.set_context(self._context):
+                config = Config(1)
             return config.gift_card_account_revenue
         return super().account_revenue_used