title: C# ZipArchive.CreateEntryFromFile() does not add file from disk to archive
body: <p>I have following code in .NET 4.5 to send email attachment using SmtpClient.
  I am adding memory stream created below to Attachement collection of message.</p>
  
  <pre><code>using System.IO;
  using System.IO.Compression;
  
  var memoryStream = new MemoryStream();
  using (var archive = new ZipArchive(memoryStream, ZipArchiveMode.Create, true))
  {
      archive.CreateEntryFromFile(@"c:\Files\File1.txt", "File1.txt");
  }
  </code></pre>
  
  <p>When I receive a email, it shows zip file but the archive does not have File1.txt. What's missing here?</p>