Slack Export users.json missing entries for external users

[camisotro]

Describe the bug My Slack history includes some channels and conversations that belong to different Slack orgs, e.g. they invited us using Slack Connect to join one of their channels. When I do a dump in Slack Export format, these users are missing from users.json completely. As a result tools like SlackLogViewer will crash on it.

To Reproduce Steps to reproduce the behavior:

1. Set up a scenario where you are on one Slack instance and another user has invited you via Slack Connect to join a channel located on their instance.
2. Use slackdump to make an export of the channel in which you chatted with them
3. Observe that the user ID attached to their messages does not appear at all in users.json

Expected behavior Even if slackdump is unable to find the user's name by API, it should ensure users.json contains an entry for every user ID that appears in exported chats. Otherwise parsing tools have difficulty with the result files.