title: wp_Query with 4 post meta feald arguments gives 500 internal server error
body: <p>I am creating a custom plugin to search for custom post type provided with 4 meta field arguments. I am using wp_Query() to fetch the search results. My Query string is.</p>
  
  <pre><code>$args = array(
          'update_post_meta_cache' =&gt; false,
          'cache_results' =&gt; false,
          'post_type' =&gt; 'caravans',
          'meta_query' =&gt; array(
              'relation' =&gt; 'OR',
              array(
                  'key' =&gt; 'caravan_used_new',
                  'value' =&gt; $used,
                  'compare'=&gt;'like',
              ),
              array(
                  'key' =&gt; 'caravan_or_motorhome',
                  'value' =&gt; $type,
                  'compare'=&gt;'like',
              ),
              array(
                  'key' =&gt; 'caravan_berth',
                  'value' =&gt; $bearth,
                  'compare'=&gt;'like',
              ),
              array(
                  'key' =&gt; 'caravan_make',
                  'value' =&gt; $make,
                  'compare'=&gt;'like',
              ),
          )
      );
      if(!empty($key)){
          $wp_query = new WP_Query("s=$key", $args);
      }else{
          $wp_query = new WP_Query($args);
      }
  </code></pre>
  
  <p>Now it is working good if I put only three meta_Query arguments when I make it to 4 its start crashing and all I see in 500 internal server error. Am I doing something wrong or meta_query has its own limits? </p>