title: wordpress custom post type pagination -- previous posts link showing when no previous posts exist
body: <p>Lots of questions about custom post types and pagination, but as far as I can find, no-one else with this problem:</p>
  
  <ul>
  <li>Post type created -- check </li>
  <li>new query for custom archive page  -- check </li>
  <li>page one totally loads correctly -- check </li>
  <li>page two shows posts it should -- check.  BUT: it also still has the <strong>previous posts</strong> link. </li>
  <li>which point to page three, even though there are no posts to display</li>
  </ul>
  
  <p>The problem:  post navigation still shows on page two, allowing for a click to page 3 (4, 5, 6 etc) -- where there are no posts. No 404, just a blank page, as though the loop is still looping through an infinite sea of nothingness. </p>
  
  <p>Code:</p>
  
  <pre><code>&lt;?php
  $paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
  $loop = new WP_Query( array(
  'post_type' =&gt; 'portfolio',
  'posts_per_page' =&gt; 10,
  'paged'=&gt;$paged
  ) ); ?&gt;
  
  &lt;?php while ( $loop-&gt;have_posts() ) : $loop-&gt;the_post(); ?&gt;
  &lt;article &gt;
  /*stuff in here */
   &lt;/article&gt;
  
  &lt;?php endwhile; ?&gt;
  
  &lt;div id="post-navigation"&gt;
  &lt;div class="nav-previous"&gt;&lt;?php next_posts_link(__( 'Previous Projects' )) ?&gt;&lt;/div&gt;
  &lt;div class="nav-next"&gt;&lt;?php previous_posts_link(__( 'Next Projects' )) ?&gt;&lt;/div&gt;
  &lt;/div&gt;&lt;!-- #post-navigation --&gt;
  </code></pre>
  
  <p>Other info:  I'm displaying this with archive-portfolio.php -- no blank page to muddy up permalinks. </p>
  
  <p>On page 1, there's no option for next post -- so that half seems to be working, but previous just lets me go back in time forever, where there are no posts to display. </p>
  
  <p>Many thanks.</p>