device/fido: don't crash when appid set with empty allowList.

Setting the AppID extension, when the authenticator supports U2F, was
sufficient to trigger the silent-probing path. But that'll crash if the
allowList is empty.

(Thank to John Bradley for finding this.)

Change-Id: I19cd6e1f93025dc01d7f7b9ff90fa6c6633bfe82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1618030
Auto-Submit: Adam Langley <agl@chromium.org>
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Cr-Commit-Position: refs/heads/master@{#661618}
2 files changed