title: How to check if Matomo was loaded or possibly blocked?
body: <p>I'm looking for a JavaScript variable, function or something to check for,
  if the Matomo tracking script wasn't successfully loaded or probably blocked (by a Tracker- or Ad-blocker browser extension, Pi-hole, etc.).</p>
  <p>I already have something similar for Google Analytics, which I want to extend:</p>
  <pre class="lang-js prettyprint-override"><code>const ehi_ga = window[window['GoogleAnalyticsObject'] || 'ga'];
  if (typeof ehi_ga !== 'function' || ehi_ga.loaded !== true || !ehi_ga.create) {
      return false;
  }
  </code></pre>
  <p>How can I extend this, to check for the existence/state of the Matomo script?</p>