added empty virtual destructor to MidiMessage class

MidiMessage.h

@@ -5,6 +5,10 @@
 class MidiMessage
 {
 public:
+    virtual ~MidiMessage() throw () 
+    {
+    }
+
 	static MidiMessage* parseMessage(std::vector<unsigned char> &messageBytes);
 
 	virtual std::vector<unsigned char> getBytes() const = 0;