Ignore unready cards

[bertschneider]

If other cards, e.g. due to internal card readers, are present, they are probably preferred and the YubiKey can not be used. Ignore unready cards and use the first available one.

Internal card readers are often present but seldom used. But they probably show up, at least that's the case on my system, before the external YubiKey and hence prevent its usage for yubikey-agent. When using the first ready card chances are much higher that it's actually the intended YubiKey.

[bertschneider]

Related to https://github.com/FiloSottile/yubikey-agent/pull/54

[smlx]

Since #54 was closed without merging it made yubikey-agent unusable for me. I now use https://github.com/smlx/piv-agent instead, you might be interested in trying that.

[bertschneider]

@smlx I didn't know that project. Thx for the hint!

[FiloSottile]

Thank you! I made a small change to ensure the Open error is not dropped on the floor.