Add a virtual desctuctor so opl handlers free correctly

Imported-from: https://svn.code.sf.net/p/dosbox/code-0/dosbox/trunk@3356

src/hardware/adlib.h

@@ -16,7 +16,7 @@
  *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  */
 
-/* $Id: adlib.h,v 1.3 2009-04-25 09:55:50 harekiet Exp $ */
+/* $Id: adlib.h,v 1.4 2009-04-26 10:33:53 harekiet Exp $ */
 
 #ifndef DOSBOX_ADLIB_H
 #define DOSBOX_ADLIB_H
@@ -105,6 +105,8 @@ public:
 	virtual void Generate( MixerChannel* chan, Bitu samples ) = 0;
 	//Initialize at a specific sample rate and mode
 	virtual void Init( Bitu rate ) = 0;
+	virtual ~Handler() {
+	}
 };
 
 //The cache for 2 chips or an opl3