webauthn: fix a crash during passkey upgrade requests

AuthenticatorRequestDialogController expects enclave_request_callback_
to be set for a passkey upgrade request. But it may not be, if GPM is
disabled via enterprise policy. Fix this by resolving the request with
an error rather than CHECK failing, if the callback is unset.

Fixed: 414750307
Change-Id: Iba23c979b097b0bcde090ea6fc78848a65b38716
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6502871
Reviewed-by: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/main@{#1454560}