fixes #2430 - fill in complete form of crm.lead on_partner_change_id triggers

Bugfix for https://github.com/odoo/odoo/issues/2430

crm.crm_case_form_view_oppor has trigger wrong function.

We can just add safely fields to on_partner_change() function because function itself checks if fields exist on targeting model. So if this function was triggered from some other models without this fields, nothing will happen because of this filter mechanism.