[FIX] hr_expense: wrong company account when creating from mail

In a multicompany environment, when a expense is created from the
expense email alias, the expense account is computed with SUPERUSER
context, so depending on the SUPERUSER set company, we could get
a mismatch of expense and employee's company and the account one, wich
causes a subsequent error when trying to post the expense.

closes odoo/odoo#63188

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