[FIX] account_voucher: Wrong entries for account voucher transaction with VAT

Steps to reproduce the bug:
- Create a vendor receipt in a journal with a foreign currency with taxes
- Validate it

Bug:

A UserError was raised because it tried to create unbalanced entries

Technically: the debit and credit of the VAT account move line were not converted
in the currency of the of the voucher's company.

opw:2007760

closes odoo/odoo#34203

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>