[FIX] base: keep company currency active

This commit aims at preventing the deactivation of a company currency.
Was the issue on 2852452 support ticket (v14). But it seems appropriate to merge it in 13.0 as it is probably a good idea that a company currency always stays active.

How to reproduce bug:
In 13.0:
Install accounting with demo data > activate multi currency in settings > deactivate usd > create new invoice > select eur currency > cannot set usd currency back on invoice

Reconcile JS traceback in 14.0:
Install accounting with demo data > activate multi currency in settings > deactivate usd > go to accounting dashboard > click on reconcile 7 items on Bank journal > click on any “customer/vendor matching” line.

closes odoo/odoo#91470

Task: 2852452
Signed-off-by: Quentin De Paoli <qdp@odoo.com>