title: second call to storeFileStream in FTPClient returns null
body: <p>I'm using apache's commons-net FTPClient to upload files.<br>
  I'm using storeFileStream method.<br>
  This works well for first call but on the second call it returns <code>null</code> and <code>.getReplyStrings()</code> returns "200 PORT command successful" !<br>
  My Code is (that is called as a method in a loop for each file):  </p>
  
  <pre><code>    FileInputStream fis = null;
      File LF=new File(localFilePath);
      InputStream is = new FileInputStream(LF);
  
      for(String DP:(remoteBasepath+"/"+remoteFilePath).split("/")){
          if(!client.changeWorkingDirectory(DP)){
              client.makeDirectory(DP);
              client.changeWorkingDirectory(DP);
          }
      }
  
      for(String line:client.getReplyStrings()){
          System.out.println(line);
      }
      OutputStream os = client.storeFileStream(LF.getName());
      byte[] buffer = new byte[1024];
      int len;
      System.out.println("start");
      long RBUN=0L;
      for(String line:client.getReplyStrings()){
          System.out.println(line);
      }
      while ((len = is.read(buffer)) != -1){
          os.write(buffer, 0, len);
          os.flush();
          RBUN+=len;
          CFPRGS.setValue(Math.round((RBUN*100/LF.length())));
      }
      for(String line:client.getReplyStrings()){
          System.out.println(line);
      }
      is.close();
      os.close();
  </code></pre>
  
  <p>What is the problem? </p>