[FIX] auth_signup: prevent traceback when mail template is not found

When user deletes 'Settings: Unregistered User Reminder' record from
'mail.template' model and when 'Users: Notify About Unregistered Users'
scheduled action is executed at that time traceback is generated on the user
side as well as in the log.

Applying this commit will fix this issue.

sentry-4174950325

closes odoo/odoo#129461

X-original-commit: 2a77e72a27ebd2bdbf32995f34d219f51d33dacf
Signed-off-by: Achraf Ben Azzouz (abz) <abz@odoo.com>

addons/auth_signup/models/res_users.py

@@ -213,6 +213,10 @@ class ResUsers(models.Model):
             _logger.info("Password reset email sent for user <%s> to <%s>", user.login, user.email)
 
     def send_unregistered_user_reminder(self, after_days=5):
+        email_template = self.env.ref('auth_signup.mail_template_data_unregistered_users', raise_if_not_found=False)
+        if not email_template:
+            _logger.warning("Template 'auth_signup.mail_template_data_unregistered_users' was not found. Cannot send reminder notifications.")
+            return
         datetime_min = fields.Datetime.today() - relativedelta(days=after_days)
         datetime_max = datetime_min + relativedelta(hours=23, minutes=59, seconds=59)
 
@@ -230,7 +234,7 @@ class ResUsers(models.Model):
 
         # For sending mail to all the invitors about their invited users
         for user in invited_users:
-            template = self.env.ref('auth_signup.mail_template_data_unregistered_users').with_context(dbname=self._cr.dbname, invited_users=invited_users[user])
+            template = email_template.with_context(dbname=self._cr.dbname, invited_users=invited_users[user])
             template.send_mail(user, email_layout_xmlid='mail.mail_notification_light', force_send=False)
 
     @api.model