This was supposed to solve the problem of losing group state after a reinstall
by inspecting member registration ids and pre-emptively sending group updates to
those who appear newly re-registered, but it has been unused since 6123c419.
Nowadays there's a protocol for requesting lost group state from other members.
// FREEBIE
Previously, updateNumbers would throw an Error, so the whole group
update was discarded.
Signal-Android handles this the same way in
GroupMessageProcessor.handleGroupUpdate().
Closes#1056
This one's been around since forever, but only manifests when someone
leaves the group and comes back. In that case we fail to reinit their
numberRegistrationId object, which causes a npe when we try to send
send them group messages.
Affected parties must ask their fickle friends to leave/join again.
// FREEBIE
