title: QMediaPlayer::metaData() can't get cover of mp3
body: <p>I set mp3 media with cover to <code>QMediaPlayer</code>, I call <code>QMediaPlayer::isMetaDataAvailable()</code> and it returns true, then I call <code>QMediaPlayer::availableMetaData()</code>, and it returns this:</p>
  
  <pre><code>("Author", "AverageLevel", "Description", "PeakValue", "Title", "WM/AlbumArtist", "WM/AlbumTitle", "WM/Composer", "WM/ContentGroupDescription", "WM/Genre", "WM/Picture", "WM/Track", "WM/TrackNumber", "WM/Year")
  </code></pre>
  
  <p>And if I call for example <code>QMediaPlayer::metaData(QMediaMetaData::Title).toString()</code> it returns correct title.
  But for some reason all of above return nothing but emptiness:</p>
  
  <pre><code>qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::CoverArtImage).toString();
  qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::CoverArtUrlLarge).toString();
  qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::CoverArtUrlLarge).toString();
  qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::CoverArtUrlSmall).toString();
  qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::PosterImage).toString();
  qDebug()&lt;&lt; player-&gt;metaData(QMediaMetaData::PosterUrl).toString();
  </code></pre>
  
  <p>I don't get why. Could anybody give me any suggestions?</p>