web admin: CSV imports (users) doesn't check presence of email

[nqb]

When you create a single user, email address is mandatory. When you use CSV import, you can create users without email addresses.

To Reproduce
Steps to reproduce the behavior:

1. Import following CSV file:

"pid","firstname"
"riss","Riss"
"luz","Luz",
"cabu","Cabu"

=> Users are created without email addresses.

Expected behavior
CSV import must not allow creation of users without email address.

[nqb]

I noticed that this check is not present when you create multiple users. In this situation, that makes sense.