Bug with joining

Description:

When a new user joins, it adds them to the default channels, which is normal. But if they change their username, their join message username link doesn't work anymore, freezing the sidebar.

Suggested Solution

Make the user tags (the clickable usernames) tied to user IDs, preventing username changes from breaking the user info page

Make the user details page (userinfo flex panel) error when it is unable to grab user details

Steps to reproduce:

1. Join a channel
2. Change your username
3. Click on the "user joined channel" message's username

Expected behavior:

Not to freeze

Actual behavior:

Freezes user info flex panel

Server Setup Information:

• Version of Rocket.Chat Server: 0.74.3
• Operating System: CentOS 7
• Deployment Method: Manual installation
• Number of Running Instances: 3
• DB Replicaset Oplog: Mongo?
• NodeJS Version: 8.15.1
• MongoDB Version: 3.4.20

Additional context

Relevant logs:

Start by reproducing the issue through the channel join message and the userinfo flex panel after changing the user's username. Trace how the clickable username is resolved and how the panel handles missing user details; done means the link remains usable after the rename and the panel does not freeze when details cannot be retrieved.