Allow when user_verification is preferred and PIN is not set

[alexandrezia]

When user_verification is "preferred" and it's not configured in ubikey, allow authentication to proceed,
As stated here: https://developers.yubico.com/WebAuthn/WebAuthn_Developer_Guide/User_Presence_vs_User_Verification.html

PREFERRED: This value indicates that the RP prefers user verification for the operation if possible, but will not fail the operation if the response does not have the AuthenticatorDataFlags.UV flag set.

[dainnilsson]

I believe the current behavior is correct: PREFERRED should be treated as REQUIRED when the Authenticator supports it (even if it isn't configured). This is in accordance with the behavior I am seeing in Windows and what I interpret from the CTAP 2 and WebAuthn specifications.