[FIX] mail: fix issue when computing `_get_recipient_data`

If we call ``MailFollowers._get_recipient_data()`` with pids parameter being
set to None there is a crash that is easily solved( list(None), should take
list fallback before hand).

Task-2739294 (Mail: Batch recipients fetch and improve its usage)

Part-of: odoo/odoo#82167

addons/mail/models/mail_followers.py

@@ -136,7 +136,7 @@ SELECT DISTINCT ON (pid) * FROM (
 ) AS x
 ORDER BY pid, notif
 """
-            params = [subtype_id, records._name, tuple(records.ids), list(pids) or []]
+            params = [subtype_id, records._name, tuple(records.ids), list(pids or [])]
             self.env.cr.execute(query, tuple(params))
             res = self.env.cr.fetchall()
         elif pids: