InstrumentPlayHandle: do not process if InstrumentTrack is muted

While regular instruments were excluded from processing when muted
this did not happen for InstrumentPlayHandle-based instruments. Muting
for exampling tracks with VSTi's inside did not decrease CPU usage.
Checking whether related InstrumentTrack is muted before calling
Instrument::play() fixes this issue.

Closes #2857426.
(cherry picked from commit 6940d19969)

include/Instrument.h

@@ -117,6 +117,8 @@ public:
 
 	virtual bool isFromTrack( const track * _track ) const;
 
+	bool isMuted() const;
+
 
 protected:
 	inline InstrumentTrack * instrumentTrack() const

include/InstrumentPlayHandle.h

@@ -1,8 +1,8 @@
 /*
- * instrument_play_handle.h - play-handle for playing an instrument
+ * InstrumentPlayHandle.h - play-handle for driving an instrument
+ *
+ * Copyright (c) 2005-2009 Tobias Doerffel <tobydox/at/users.sourceforge.net>
  *
- * Copyright (c) 2005-2008 Tobias Doerffel <tobydox/at/users.sourceforge.net>
- * 
  * This file is part of Linux MultiMedia Studio - http://lmms.sourceforge.net
  *
  * This program is free software; you can redistribute it and/or
@@ -22,7 +22,6 @@
  *
  */
 
-
 #ifndef _INSTRUMENT_PLAY_HANDLE_H
 #define _INSTRUMENT_PLAY_HANDLE_H
 
@@ -46,7 +45,10 @@ public:
 
 	virtual void play( sampleFrame * _working_buffer )
 	{
-		m_instrument->play( _working_buffer );
+		if( !m_instrument->isMuted() )
+		{
+			m_instrument->play( _working_buffer );
+		}
 	}
 
 	virtual bool done() const