gui: PreviewGeneratorMapFunctor: Use PreviewGenerator::get()

gui/previewgeneratormapfunctor.h

@@ -14,16 +14,12 @@ class PreviewGeneratorMapFunctor
 		LAST_DUMMY
 	};
 	RenderConfig renderConfig;
-	PreviewGenerator *generator[LAST_DUMMY];
-	PreviewGenerator *getGenerator(QString filePath);
 
   public:
 	typedef QSharedPointer<PreviewResult> result_type;
 
 	PreviewGeneratorMapFunctor();
 
-	~PreviewGeneratorMapFunctor();
-
 	void setRenderConfig(RenderConfig config);
 
 	QSharedPointer<PreviewResult> operator()(const QSharedPointer<PreviewResult> &renderResult);