Fix custom Group MMS names
Unfortunately, I needed https://source.puri.sm/kop316/chatty/-/commits/wip/group_mms_detail to uncover this issue, as it was a bit complex.
Group MMS had a name by default, so chatty_mm_chat_update_contact ()
could never run, and chatty_mm_chat_update_contact ()
should run regardless of having a custom name or not because of https://source.puri.sm/kop316/chatty/-/commits/wip/group_mms_detail showing contacts.
In this manner, the title will only be updated if there is a custom name and the contacts will update