Fix isGoodSignature
GPGME_SIG_STAT_GOOD is not a flag but an enum so using & will result in wrong values with GPGME_SIG_STAT_NOKEY and GPGME_SIG_STAT_ERROR
GPGME_SIG_STAT_GOOD is not a flag but an enum so using & will result in wrong values with GPGME_SIG_STAT_NOKEY and GPGME_SIG_STAT_ERROR