title: Problems after installation of TYPO3 extension pits_downloadcenter
body: <p>I'm using TYPO3 9.5.5 and have installed pits_downloadcenter 3.0.1 extension.<br>
  I am encountering errors after installation in 'Extensions Manager'.</p>
  
  <blockquote>
    <p>Call to a member function admin_get_tables() on null"
    in "typo3conf/ext/pits_downloadcenter/class.ext_update.php line 68"</p>
  </blockquote>