[FIX] account: Fix rate when reconciling

Introduced by:
https://github.com/odoo/odoo/commit/ba82fbe1b08108178a9fd7bade82b625c987e36e



The rate of the opposite line must remain the same when fallbacking on the company currency.

closes odoo/odoo#132213

Signed-off-by: Brice Bartoletti (bib) <bib@odoo.com>