csync_vio_local_stat: Win: fetch mtime and size if not previously fetched

csync_vio_local_stat: Win: fetch mtime and size if not previously fetched

Since owncloud 2.1, csync_vio_local_stat was optimized because readdir
would already fetch most of the info.  This works for the discovery,
but not later.  And we used this function later for symliks and co.

So this fixes the .lnk on windows

Issue #4300