title: If Loader's sourceComponent Item references its parent, and I set "loader.active = false", I get an error
body: <p>My code:</p>
  
  <pre><code>import QtQuick 2.6
  import QtQuick.Window 2.2
  
  Window {
      visible: true
      width: 640
      height: 480
  
      Item {
          id: loaderParent
          Loader {
              id: loader
              active: true
              sourceComponent: Item {
                  parent: loaderParent
                  x: parent.x
              }
          }
      }
  
      Item {
          focus: true
          Keys.onPressed: {
              loader.active = false;
          }
      }
  }
  </code></pre>
  
  <p>When I press any key, I get this error:</p>
  
  <blockquote>
    <p>qrc:/main.qml:16: TypeError: Cannot read property of null</p>
  </blockquote>
  
  <p>Thought I suspect this error is harmless, I'd like an explanation or any idea for a fix/workaround?</p>
  
  <p>Reported <a href="https://bugreports.qt.io/browse/QTBUG-61853" rel="nofollow noreferrer">here</a>.</p>