don't delete current Song's steps through the LastSaved when destructing ScreenEdit

stepmania/src/ScreenEdit.cpp

@@ -613,6 +613,9 @@ void ScreenEdit::Init()
 
 ScreenEdit::~ScreenEdit()
 {
+	// UGLY: Don't delete the Song's steps.
+	m_songLastSave.DetachSteps();
+
 	LOG->Trace( "ScreenEdit::~ScreenEdit()" );
 	m_soundMusic.StopPlaying();
 }

stepmania/src/Song.cpp

@@ -85,6 +85,13 @@ Song::~Song()
 	// that all pointers to this Song and its Steps are invalidated.
 }
 
+void Song::DetachSteps()
+{
+	m_vpSteps.clear();
+	FOREACH_StepsType( st )
+		m_vpStepsByType[st].clear();
+}
+
 /* Reset to an empty song. */
 void Song::Reset()
 {

stepmania/src/song.h

@@ -59,6 +59,7 @@ public:
 	Song();
 	~Song();
 	void Reset();
+	void DetachSteps();
 
 	NotesLoader *MakeLoader( CString sDir ) const;