Fix from dadkins: diroffset never resets to 0 on multiple dirreads from the same open dir.
Fix from dadkins: diroffset never resets to 0 on multiple dirreads from the same open dir.

Fixes issue 6

henesy/go9p,cleahcim/go9p,edahlgren/go9p,szhilkin/go9p,larsth/go9p,nigifabio/go9p,nilium/go9p,henesy/go9p,nilium/go9p,lionkov/ninep,floren/go9p,larsth/go9p,KevinMGranger/go9p,floren/go9p,szhilkin/go9p,KevinMGranger/go9p,nigifabio/go9p,cleahcim/go9p