invite command, when it can't resolve all people, should either do its best or do nothing, but not do a partial run

[reivilibre]

When you hit some users that don't have any e-mail address or Matrix ID, some users will be invited and the overall process will fail with Failed to resolve all targets for auditorium.

Ideally the bot should either do its utmost best (ignore only the problematic users) or check this all upfront (and do nothing) — as it stands, it's quite misleading.