title: WebClient DownloadFileAsync File Exists
body: <p>Is there a recommended method for using DownloadFileAsyc and determining if the file exists? It seems that the only way I can tell is on the DownloadCompleted event the error property has a 404 error in it, and the there's a file created that is 0 bytes. </p>
  
  <p>It would be nice to have a more deterministic method.</p>