Make 1.6+ work with new instance format.

logic/tasks/ProgressProvider.h

@@ -32,6 +32,7 @@ signals:
 	void status(QString status);
 
 public:
+	virtual ~ProgressProvider() {};
 	virtual QString getStatus() const = 0;
 	virtual void getProgress(qint64 &current, qint64 &total) = 0;
 	virtual bool isRunning() const = 0;