Ensure clips that have a valid track container are added to it

src/gui/clips/SampleClipView.cpp

@@ -363,6 +363,7 @@ bool SampleClipView::splitClip( const TimePos pos )
 		m_clip->getTrack()->saveJournallingState( false );
 
 		auto rightClip = new SampleClip(*m_clip);
+		m_clip->getTrack()->addClip(rightClip);
 
 		m_clip->changeLength( splitPos - m_initialClipPos );