title: PhantomJS skip header on first page
body: <p>I want to remove header from first page and I have header defined as:</p>
  
  <pre><code>header = {
      height: header_height,
      contents: phantom.callback(function(pageNum, numPages) {
          if(pageNum == 1) {
              return "";
          }
          return header_contents;
      })
  };
  </code></pre>
  
  <p>But it lefts empty margin with <code>header_height</code>. Are there any way to set <code>header.height=0</code> for first page?</p>