fix DifficultyIcon hiding when no song is selected

(Note that in general, actors should never SetHidden(false) on themselves,
since that will cause themed "hidden,1" commands to be overridden.)

stepmania/src/DifficultyIcon.cpp

@@ -26,6 +26,10 @@
 #include "RageDisplay.h"
 #include "arch/ArchHooks/ArchHooks.h"
 
+DifficultyIcon::DifficultyIcon()
+{
+	m_bBlank = false;
+}
 
 bool DifficultyIcon::Load( CString sPath )
 {
@@ -48,13 +52,14 @@ bool DifficultyIcon::Load( CString sPath )
 void DifficultyIcon::SetFromNotes( PlayerNumber pn, Steps* pNotes )
 {
 	if( pNotes == NULL )
-		SetHidden(true);
+		m_bBlank = true;
 	else
 		SetFromDifficulty( pn, pNotes->GetDifficulty() );
 }
 
 void DifficultyIcon::SetFromDifficulty( PlayerNumber pn, Difficulty dc )
 {
+	m_bBlank = false;
 	switch( GetNumStates() )
 	{
 	case NUM_DIFFICULTIES:		SetState( dc );			break;
@@ -65,6 +70,7 @@ void DifficultyIcon::SetFromDifficulty( PlayerNumber pn, Difficulty dc )
 
 void DifficultyIcon::SetFromCourseDifficulty( PlayerNumber pn, CourseDifficulty cd  )
 {
+	m_bBlank = false;
 	switch( cd )
 	{
 	case COURSE_DIFFICULTY_REGULAR:		SetFromDifficulty(pn,DIFFICULTY_MEDIUM);	break;

stepmania/src/DifficultyIcon.h

@@ -19,7 +19,12 @@ class Steps;
 
 class DifficultyIcon : public Sprite
 {
+	bool m_bBlank;
+
 public:
+	DifficultyIcon();
+	virtual bool EarlyAbortDraw() { return m_bBlank || Sprite::EarlyAbortDraw(); }
+
 	bool Load( CString sFilePath );
 
 	void SetFromNotes( PlayerNumber pn, Steps* pNotes );

stepmania/src/ScreenSelectDifficultyEX.h

@@ -17,7 +17,6 @@
 #include "RandomSample.h"
 #include "ScreenSelect.h"
 #include "Sprite.h"
-#include "DifficultyIcon.h"
 #include "OptionsCursor.h"
 
 class ScreenSelectDifficultyEX : public ScreenSelect