[FIX] im_livechat: correctly display known partner name

When talking via the Live Chat to a known partner, should be able to see
his name in the chat window title, from the commit: c04b9c01
the partner name wasn't showing in the title as sudo is being used.

After this commit, known partner name will be shown in the
Live Chat window title.

And improving a test case, in which we're checking for the known partner's
name in the chat window title.

task-1940407

closes odoo/odoo#33831

Signed-off-by: Martin Geubelle (mge) <mge@openerp.com>