Invalid “UTF8 Names Validation” regexp breaks channels

Description:

Server Setup Information:

• Version of Rocket.Chat Server: 0.59.3
• Operating System: Linux
• Deployment Method(snap/docker/tar/etc): Rocket Chat Cloud
• Number of Running Instances: ?
• DB Replicaset Oplog: ?
• Node Version: v4.8.4

Steps to Reproduce:

1. Go to administrative UI » General » UTF8
2. Enter an invalid regular expression, such as: /([0-9a-zæøåA-ZÆØÅ-_.]+)/
3. Save.
4. Reload normal UI.
5. Click a channel.

Expected behavior:

One of two options:

1. The UI works as normal, but now allows channel names containing the Danish special characters Æ, Ø and Å.
2. Otherwise, I get an error when attempting to save the setting due to its invalid value.

Actual behavior:

The setting is saved, and I get the following JavaScript error when rendering channels:

SyntaxError: Invalid regular expression: /@([0-9a-zæøåA-ZÆØÅ-_.]+)/: Range out of order in character class

The error breaks channel rendering completely.

Relevant logs:

I no longer have any relevant logs, sorry.

Start in the administrative UI's General » UTF8 setting and trace how the saved regular expression is consumed when rendering channels. Reproduce with /([0-9a-zæøåA-ZÆØÅ-_.]+)/ and verify that an invalid expression is rejected on save or that valid Danish characters work without breaking channel rendering.