[FIX] stock: on partial picking, do no open a new window action if not needed

This is related to rev. dd4d72d

Not opening a new window action allows to keep the current list of stock picking being threated, and to use the next an previous arrow of the forom view of the web client.
Merge branch '7.0' of https://github.com/odoo/odoo into 7.0-win32