MFC r216084:

MFC r216084:

Don't panic when we read an empty ACL from ZFS.  Apparently this may happen
with filesystems created under MacOS X ZFS port.  This is kind of filesystem
corruption (we don't allow for setting empty ACLs), so make acl_get_file(3)
and related syscalls fail with EINVAL in that case.  In theory, we could
return empty ACL to userland, but I'm afraid this would break some code.

Approved by:	re (kib)

git-svn-id: svn://svn.freebsd.org/base/stable/8@216271 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f