configfile: overwrite and let keys run out of scope
configfile: overwrite and let keys run out of scope

As soon as we don't need them anymore, overwrite
keys with zeros and make sure they run out of scope
so we don't create a risk of inadvertedly using all-zero
keys for encryption.

https://github.com/rfjakob/gocryptfs/issues/211

rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs