server doesn't support walk with empty wnames

[gdevillele]

Even if the 9p protocol allows for walking with no wnames, go9p server implementation will generate an error.

9p documentation : http://man.cat-v.org/plan_9/5/walk
Quote:
It is legal for nwname to be zero, in which case newfid will represent the same file as fid and the walk will usually succeed; this is equivalent to walking to dot.

IMHO, the change should be done in func (srv *Srv) walkPost(req *Req)