[FIX] sale: Keep fiscal position from SO
[FIX] sale: Keep fiscal position from SO

Steps to reproduce the bug:
- Create two fiscal postions fp1 and fp2
- Create a customer C with fp1
- Create a SO for C and set fp2
- Create an invoice for the SO

BUG:

The fiscal position of the SO was set to False.
Now the fiscal position of the SO is kept when creating an invoice
from a SO.

opw:1963910

closes odoo/odoo#32713

Signed-off-by: Simon Goffin (sig) <b3ed2cf313e7546085c3c50622143ff31e467d23@openerp.com>
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo