[FIX] account: duplicate journal entry

When a journal entry includes taxes, it is impossible to duplicate it
because of an unbalanced entry error.
Indeed, by default the taxes are computed at the creation of the account
move lines, leading to the creation of a new tax line, therefore
unbalancing the account move.

Fixes #11919
opw-676788

addons/account/models/account_move.py

@@ -101,6 +101,10 @@ class AccountMove(models.Model):
         move.assert_balanced()
         return move
 
+    @api.multi
+    def copy(self, default=None):
+        return super(AccountMove, self.with_context(dont_create_taxes=True)).copy(default)
+
     @api.multi
     def write(self, vals):
         if 'line_ids' in vals: