[FIX] mass_mailing: correctly find partner email in mass mailing
[FIX] mass_mailing: correctly find partner email in mass mailing

In mass mailing access to partners when performing a mass mailing has been
done in batch to speedup computation [1]. Emails are put into a dictionary
allowing to find back the email based on partner_id.

However the matching between the partner and its emails is done using a
shortcut using the current document ID as partner ID. It works when performing
a mass mailing on partners but fails when performing a mass mailing on models
having message_get_default_recipients not returning only emails. Currently
in saas-14 main models return only emails (crm, event, mailing contacts) but
other models may encounter issues (applicants, tickets).

This commit fixes it by correctly matching partner id and its found email.

Related to task ID 1924711
Linked to PR #32496

[1] See 65ed4553a50fdbefc986b7d21f87a81c42b743c7
ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo