Check if track container exists before deleting track from it

src/core/Track.cpp

@@ -84,7 +84,7 @@ Track::~Track()
 		delete m_clips.back();
 	}
 
-	m_trackContainer->removeTrack( this );
+	if (m_trackContainer) { m_trackContainer->removeTrack(this); }
 	unlock();
 }