之前似乎没考虑到这种情况

Required before beta 16

Bug Report

Current Behavior
Because of flarum/framework#2713, the Activated event runs multiple time. This extension always adds the group every time the event is dispatched without checking if the user already has the group.

Steps to Reproduce
I have not reproduced myself but the error has been seen here clarkwinkelmann/flarum-ext-passwordless#9

It should be reproducible by changing email and validating new email, or by logging in with the Passwordless extension.

It results in an error like Integrity constraint violation: 1062 Duplicate entry '1-6' for key 'PRIMARY' trying to re-insert the same group-user relationship.

Environment

• Flarum version: 1.0.x

Possible solution(s)
We need to check whether the group is already added in https://github.com/FriendsOfFlarum/default-group/blob/master/src/Listeners/AddDefaultGroup.php

Even if the issue about duplicate event is fixed in Flarum, this is still a necessary fix in case a different extension would add the same group before this extension runs.