[FIX] account: Validating a statement with old posted moves

When validating a statement with old posted moves, the lock date
was checked by function, _check_lock_date and then it was impossible
to validate the statement even if all the moves were already posted.

addons/account/models/account_bank_statement.py

@@ -241,7 +241,7 @@ class AccountBankStatement(models.Model):
                 for aml in st_line.journal_entry_ids:
                     moves |= aml.move_id
             if moves:
-                moves.post()
+                moves.filtered(lambda m: m.state != 'posted').post()
             statement.message_post(body=_('Statement %s confirmed, journal items were created.') % (statement.name,))
         statements.link_bank_to_partner()
         statements.write({'state': 'confirm', 'date_done': time.strftime("%Y-%m-%d %H:%M:%S")})