Fix access picking type on purchase requisition.

Fix issue #3807

Requisition picking type is by default the incoming picking type created from stock module...if you have a multicompany database this will generate all the time an error because the first picking type for receipt is assigned to the first warehouse, and other companies will use their warehouses...you will not have read access to the picking type.

Code extracted from the purchase.order from the same function.

Could you review this @jco-odoo , please.