Fixes #2624 ("Controls window of LFO controller is not destroyed upon

closing a project")

When it is destroyed the ControllerView now deletes the controller sub
window in case it has one.

src/gui/widgets/ControllerView.cpp

@@ -104,6 +104,10 @@ ControllerView::ControllerView( Controller * _model, QWidget * _parent ) :
 
 ControllerView::~ControllerView()
 {
+	if (m_subWindow)
+	{
+		delete m_subWindow;
+	}
 }