[FIX] mass_mailing: fix batch call of action_send_mail

Loop inner calls should use mailing not self.

Task ID-2455433

closes odoo/odoo#65755

X-original-commit: d63734eb6e00c079ad9c0658674efb2321610173
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mass_mailing/models/mailing.py

@@ -617,7 +617,7 @@ class MassMailing(models.Model):
             composer_values = {
                 'author_id': author_id,
                 'attachment_ids': [(4, attachment.id) for attachment in mailing.attachment_ids],
-                'body': self._prepend_preview(self.body_html, self.preview),
+                'body': mailing._prepend_preview(mailing.body_html, mailing.preview),
                 'subject': mailing.subject,
                 'model': mailing.mailing_model_real,
                 'email_from': mailing.email_from,
@@ -633,7 +633,7 @@ class MassMailing(models.Model):
                 composer_values['reply_to'] = mailing.reply_to
 
             composer = self.env['mail.compose.message'].with_context(active_ids=res_ids).create(composer_values)
-            extra_context = self._get_mass_mailing_context()
+            extra_context = mailing._get_mass_mailing_context()
             composer = composer.with_context(active_ids=res_ids, **extra_context)
             # auto-commit except in testing mode
             auto_commit = not getattr(threading.currentThread(), 'testing', False)