Fix issues #18 #19 #20 

https://github.com/zfsrogue/zfs-crypto/issues/20 Keysource file does not work - key can not be of zero size

https://github.com/zfsrogue/zfs-crypto/issues/19 zfs clone fails with segfault 

https://github.com/zfsrogue/zfs-crypto/issues/18 zfs send/receive fails - cannot receive new filesystem stream: pool must be upgraded to receive this stream