Following 4de3795, as now `tag_ids` are not lost, the comparison is incorrect due to
partner not having category_id, and then keep it previous tags in mass mailing contact.
We add this check for avoiding problems.
Without this patch, users without access to reading and editing mass mailing contact records are now unable to change a partner's name or email. They'd recieve an exception such as:
AccessError: Sorry, you are not allowed to access this document. Only users with the following access level are currently allowed to do that:
- Mass Mailing/User
(Document model: mail.mass_mailing.contact)
Restrictive ACLs shouldn't restrict normal user operation nor DB consistency, so using sudo mode now and testing behavior.