[FIX] purchase: enable correct currency on onchange partner_id

Steps to reproduce:
- company currency = USD
- set a partner P with a `property_purchase_currency_id` in EUR
- create a bill with Azure partner and set an bill line
- change to partner P
issue -> the currency of the line has not been change
- change to Azure
issue -> no change about the currency

Cause:
- We update the move.currency_id but not the line_ids.currency_id
- after setting Partner P, we try to set a partner that no `property_purchase_currency_id`, we do not enter in the condition

opw-3233527

closes odoo/odoo#116852

Signed-off-by: Cedric Snauwaert <csn@odoo.com>