500 Internal Server Error if the options page is requested for a non-existent user

https://bugs.launchpad.net/mailman/+bug/1961762

Commits that fix the bug:

• https://bazaar.launchpad.net/~mailman-coders/mailman/2.1/revision/1887
• https://bazaar.launchpad.net/~mailman-coders/mailman/2.1/revision/1888

And there are other commits following these above that seem interesting too:

https://code.launchpad.net/~mailman-coders/mailman/2.1