title: reviewboard post-review and "A +" status files
body: <p>I have some "A  +" status files after merge from another branch in my svn work path,
  like this:</p>
  
  <pre><code>M      .
  A  +    protected/extensions/Everyman/neo4jphp.phar
  A  +    protected/extensions/Everyman/InitNeo4j.php
  A  +    protected/extensions/Everyman/README
  </code></pre>
  
  <p>When I submit a review by using post-review, upload diff failed:</p>
  
  <pre><code>Error uploading diff
  
  Your review request still exists, but the diff is not attached.
  </code></pre>
  
  <p>and the debug log show</p>
  
  <blockquote>
    <blockquote>
      <blockquote>
        <p>Got API Error 219 (HTTP code 400): The specified diff file is empty</p>
      </blockquote>
    </blockquote>
  </blockquote>
  
  <p>when i try get diff to upload using svn diff, bug get nothing</p>
  
  <p>How can I post a review for these "A  +" status files?</p>