No invitation link after adding a new user when email server is not configured

[gabrieldutra]

Issue Summary

After #3267 and #3229 admins no longer receive a link to invite users when the server doesn't have an email server configured.

Steps to Reproduce

1. Open /users/new in a server without email configured (e.g.: preview)
2. Create a new user and check that no link is provided.
3. Open the pending invitation User Profile and notice there's only the "Resend" option (again it leads to nowhere)

Any other info e.g. Why do you consider this to be a bug? What did you expect to happen instead?
The admin should receive a link to send to the user manually.

Technical details:

• Redash Version: Latest (Redash Preview)
• Browser/OS: --
• How did you install Redash: --