[FIX] mail: avoid re-reading a value given to create

After a message is created with a given `author_id`, reuse `author_id` instead
of `message.author_id.id`.

addons/mail/models/mail_thread.py

@@ -1900,8 +1900,8 @@ class MailThread(models.AbstractModel):
             if not subtype_rec.internal:
                 # done with SUPERUSER_ID, because on some models users can post only with read access, not necessarily write access
                 self.sudo().write({'message_last_post': fields.Datetime.now()})
-        if new_message.author_id and model and self.ids and message_type != 'notification' and not self._context.get('mail_create_nosubscribe'):
-            self.message_subscribe([new_message.author_id.id], force=False)
+        if author_id and model and self.ids and message_type != 'notification' and not self._context.get('mail_create_nosubscribe'):
+            self.message_subscribe([author_id], force=False)
 
         self._message_post_after_hook(new_message)
 

odoo/addons/test_performance/tests/test_performance.py

@@ -141,7 +141,7 @@ class TestPerformance(TransactionCase):
 
         records.write({'value': self.int(20)})
 
-    @queryCount(admin=20, demo=33)
+    @queryCount(admin=19, demo=29)
     def test_write_mail_with_tracking(self):
         """ Write records inheriting from 'mail.thread' (with field tracking). """
         record = self.env['test_performance.mail'].search([], limit=1)
@@ -180,7 +180,7 @@ class TestPerformance(TransactionCase):
         model = self.env['test_performance.mail']
         model.with_context(tracking_disable=True).create({'name': self.str('X')})
 
-    @queryCount(admin=40, demo=58)
+    @queryCount(admin=39, demo=55)
     def test_create_mail_with_tracking(self):
         """ Create records inheriting from 'mail.thread' (with field tracking). """
         model = self.env['test_performance.mail']