Only display « Migrating devices of user » for users who actually have u2f keys in migration

[tcitworld]

Steps to reproduce

1. Have a lot of users
2. Execute php occ twofactor_webauthn:migrate-u2f --all

Expected behaviour

The message Migrating devices of user X should only be displayed for users with actual u2f keys registered.

Actual behaviour

The message is displayed for all users, even if they don't have any registered u2f keys to migrate

Fix

An easy fix is to make sure the following line only executes if count($registrations) > 0.

twofactor_webauthn/lib/Command/MigrateU2F.php

Line 123 in 419dc09

$output->writeln('Migrating devices of user ' . $user->getUID());