title: muplugins_loaded hook is not triggered
body: <p>I am creating my very first Wordpress plugin. I intend to make this a wrapper, so it should be initialized before other elements are initialized and finalized after other elements are finalized.</p>
  
  <p>I have been researching the actions <a href="https://codex.wordpress.org/Plugin_API/Action_Reference" rel="nofollow">here</a> and thought <a href="https://codex.wordpress.org/Plugin_API/Action_Reference/muplugins_loaded" rel="nofollow">muplugins_loaded</a> and <a href="https://codex.wordpress.org/Plugin_API/Action_Reference/shutdown" rel="nofollow">shutdown</a> should be the right events for my scenario.</p>
  
  <p><code>muplugins_loaded</code> is supposed to be executed</p>
  
  <blockquote>
    <p>After must-use plugins are loaded</p>
  </blockquote>
  
  <p>so, I have a code like this:</p>
  
  <pre><code>defined( 'ABSPATH' ) or die( 'No script kiddies please!' );
  
  //Checking whether queries are to be saved
  if ( defined( 'SAVEQUERIES' ) &amp;&amp; SAVEQUERIES ) {
  
      //definition of the WordpressBenchmarker class    
  
      function initWordpressBenchmark() {
          WordpressBenchmarker::initialize();
      }
  
      function finalizeWordpressBenchmark() {
          WordpressBenchmarker::finish();
      }
  
      add_action( 'muplugins_loaded', 'initWordpressBenchmark', 1 );
      add_action( 'shutdown', 'finalizeWordpressBenchmark', 20 );
  
  }
  </code></pre>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>Call to a member function finalize() on a non-object in</p>
  </blockquote>
  
  <p>which clearly points to this line:</p>
  
  <pre><code>WordpressBenchmarker::finish();
  </code></pre>
  
  <p>which, believe me that surely means that <code>initWordpressBenchmark</code> was not executed. This makes me think that the plugin was not executed because it is not a must used plugin. Should I make it a must used plugin? Is there a better way? As an alternative I am thinking using the <code>plugins_loaded</code> hook with a value which is smaller than any other values. After searching for references for <code>plugins_loaded</code> I have seen that the smallest number for priorities was 0. I am wondering whether a negative value as the priority</p>
  
  <pre><code>add_action( 'plugins_loaded', 'initWordpressBenchmark', -1 );
  </code></pre>
  
  <p>would be a good solution.</p>