title: CodeIgniter - force_download() no output
body: <p>Fast to explain, but I can't get it to work:</p>
  
  <p>In this simple code, the function force_download simply doesn't make any output.</p>
  
  <pre><code>$this-&gt;load-&gt;helper('download');
  $data = file_get_contents("modulos/".$filename); // Read the file's contents
  force_download($filename, $data);
  echo $data."/".$filename;
  </code></pre>
  
  <p>Here I just get a white screen, but the file content is show (well you know, the strange codified content :)
  I think it is simple enough, I just want the file downloaded with no other effect, am I doing something wrong?</p>