The placeholders were rendered as empty string in the web version of the
mailing (accessed through the "view online" link in the email). This fixes the
problem.
Technical note: we cannot use mail_mail.body_html (which contains already the
rendered placeholder for the specific user) as it is marked for deletion so we
render it from mailing_mailing.body_html.
Task-2954282
closesodoo/odoo#100984
X-original-commit: 6b2d5db762ef198e9f07af95116c166b027eb383
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>