[FIX] mass_mailing_*: Improve error handling for missing redirect URL

Handling of 'None' return value from 'get_url_from_code' to
prevent crashes in 'request.redirect'

https://github.com/odoo/odoo/blob/05fc9a67335d5a96752d828defa066d4fdabe301/addons/link_tracker/models/link_tracker.py#L248-L255

Apply same logic as

https://github.com/odoo/odoo/blob/c46f4b908a73658ce2aa7fd9987fbac76a0dda00/addons/link_tracker/controller/main.py#L21-L24



sentry-4183731887

closes odoo/odoo#121405

Signed-off-by: Achraf (abz) <abz@odoo.com>