handle deleting configuration better
handle deleting configuration better

if both slots are configured and one is deleted programming sequence will be
counted up as usual. when the last slot is deleted programming sequence will
be set to 0. try to handle this.

eworm-de/yubikey-personalization,dmitriykuptsov/yubikey-personalization,Yubico/yubikey-personalization,Yubico/yubikey-personalization,eworm-de/yubikey-personalization,dmitriykuptsov/yubikey-personalization,Yubico/yubikey-personalization-dpkg,dmitriykuptsov/yubikey-personalization,Yubico/yubikey-personalization-dpkg,Yubico/yubikey-personalization-dpkg,eworm-de/yubikey-personalization