title: Git: Internal error: refs/remotes/origin/master is not a valid packed reference
body: <p>I am attempting to clone a git repository on a Windows network drive, but the process fails. It first throws a <code>internal error: refs/remotes/origin/master is not a valid packed reference</code>, and then repeatedly relates that it failed to unlink an index file.</p>
  
  <pre><code>x:\code\source&gt; git clone x:\code\repos\project.git
  Cloning into 'project'...
  done.
  error: internal error: refs/remotes/origin/master is not a valid packed reference!
  fatal: update_ref failed for ref 'HEAD': cannot update the ref 'HEAD': 
    Trying to write ref refs/heads/master with nonexistent object d34950c3faee46d8a7f3b8e7950b04fcc5da9d1c
  Unlink of file 'project/.git/objects/pack/pack-....idx' failed. Should I try again? (y/n)
  </code></pre>
  
  <p>I am able to clone without issue to a local drive from a bare repo on the network drive, but am unable to clone to a network drive.</p>