better fix for 6726630, which helps zfs cmd

[anthony.scarp...@sun.com]

Author: Anthony Scarpino <Anthony.Scarpino at Sun.COM>
Repository: /hg/zfs-crypto/gate
Latest revision: 184bd7a105810e0aff286b697faf4b6144117b0f
Total changesets: 1
Log message:
better fix for 6726630, which helps zfs cmd

Files:
        update: usr/src/lib/libzfs/common/libzfs_crypto.c