[FIX] base: user partner must be kept global on company switch

Introduced when migrating base to new API with 7eab8e2.

closes #14374
opw-694319

openerp/addons/base/res/res_users.py

@@ -359,7 +359,7 @@ class Users(models.Model):
         if 'company_id' in values:
             for user in self:
                 # if partner is global we keep it that way
-                if user.partner_id.company_id.id != values['company_id']:
+                if user.partner_id.company_id and user.partner_id.company_id.id != values['company_id']:
                     user.partner_id.write({'company_id': user.company_id.id})
             # clear default ir values when company changes
             self.env['ir.values'].get_defaults_dict.clear_cache(self.env['ir.values'])