Error with partner fiscal position

An error is raised when changing the customer of a quotation if he has a specific fiscal position.

***Impacted versions:***

 - 8.0, master

***Steps to reproduce:***

 1. Create a fresh database, create a new customer and set his fiscal position.
 2. Create a quotation, select the customer

***Current behavior:***

File "/Users/keje/src/odoo/addons/account/partner.py", line 107, in get_fiscal_position
    return part.property_account_position.id
NameError: global name 'part' is not defined

***Expected behavior:***

No error