Proposed fix for https://github.com/alexeypetrushin/vos/issues/1

Allow empty home because some servers allow SFTP access (now SSH shell)
only.

Not sure if this has any unwanted side-effects but 
1) it works for me :-) and 
2) the raised error is not helpful in any situation i can imagine. this happens after successful authentication in any case.

So please consider pulling this.