[FIX] stock_dropshipping: Creating a quotation without purchase permission

Fine tuning of this commit: f93fcaff

Steps to reproduce the bug:

- Open runbot v11
- Restrict Demo's access to Sales Manager for sales and employee for Employee
- Try to create a new quotation

Bug:
- You got Odoo server Error
Sorry, you are not allowed to access this document. Only users with the following access level are currently allowed to do that:
- Inventory/User
- Accounting & Finance/Billing
- Purchases/User
- Purchases/Manager
- Other Extra Rights/Portal
(Document model: purchase.order.line) - (Operation: read, User: 5)

opw:2120692

closes odoo/odoo#40153

X-original-commit: 1b14af28
Signed-off-by: Simon Goffin (sig) <sig@openerp.com>