Set the proper company_id on an imported partner

When a partner is being imported, the company id is not set, which leaves the choice to the system. While there is another solution proposed in #52, this makes things work until someone has the time to fix multicompany issues properly.
Not sure I follow, if it does not pass either 'if', then it would be as if the code was not there at all and everything stays as it was (setting it according the running user). Or are you suggesting returning {'company_id': False} in that case?