deleteLater() called to QMediaPlayer from its signal handler does not work as expected

When deleteLater() is called to QMediaPlayer object from a slot attached to the player's mediaStatusChanged signal the player is not deleted next time the event loop spins.

The attached test case added to qtmultimedia/tests/auto/integration/qmediaplayerbackend reproduces the problem.

This issue has the same root cause as https://bugreports.qt-project.org/browse/QTBUG-18434. The QMediaPlayer::mediaStatusChanged signal is eventually emitted directly from a GStreamer/GLib message callback, not from Qt event loop.