Comment 8 for bug 7427

A thought about how to make this less bad in a simple way: if the attempt to
automatically generate a username produces something that isn't usable, then
simply don't try to automatically generate the username, and leave it blank.
This would mean that at least somebody entering "José" as their first name would
not be presented with the invalid "josé" username. Since ASCII transliteration
might in some cases be very difficult (consider names in non-Latin scripts),
this is probably the best we can do until full Unicode usernames are safe
everywhere.