bug fix: interator on v0 and v1 is not OK.
bug fix: interator on v0 and v1 is not OK.

When create a new itertor, it might be possible that the key is the
special value for EMPTY or DELETE, i.e. v0 and v1. The original
implemention didn't handle this properly.

wcy123/vhash,wcy123/vhash