Master password: Make sure accounts without password are included

[mickenordin]

Previously only accounts with a password set would be provisioned with the master password, this patch fixes that.

One potential problem with this patch is that it copies a function from here:

https://github.com/nextcloud/mail/blob/c1e332d163302590c8ad6a2292951f224a1497bb/lib/Service/Provisioning/Manager.php#L358-L375

If we make that function public in the provisioning manager, we could reuse the code better, so that might be something to consider.

Edit: This concern is addressed now.