sftp: fix test failures

This was introduced by 50a3a96e27

cmd/serve/sftp/handler.go

@@ -93,8 +93,9 @@ func (v vfsHandler) Filecmd(r *sftp.Request) error {
 		// link := newMemFile(r.Target, false)
 		// link.symlink = r.Filepath
 		// v.files[r.Target] = link
-	}
 		return sftp.ErrSshFxOpUnsupported
+	}
+	return nil
 }
 
 type listerat []os.FileInfo