Clear the popup on scene clear

Fixes #257

src/GUI/graphicsscene.cpp

@@ -46,3 +46,9 @@ void GraphicsScene::helpEvent(QGraphicsSceneHelpEvent *event)
 
 	/* No need to process QGraphicsScene::helpEvent() */
 }
+
+void GraphicsScene::clear()
+{
+	Popup::clear();
+	QGraphicsScene::clear();
+}

src/GUI/graphicsscene.h

@@ -18,6 +18,9 @@ class GraphicsScene : public QGraphicsScene
 public:
 	GraphicsScene(QObject *parent = 0) : QGraphicsScene(parent) {}
 
+public slots:
+	void clear();
+
 protected:
 	void helpEvent(QGraphicsSceneHelpEvent *event);
 

src/GUI/popup.cpp

@@ -163,3 +163,9 @@ void Popup::show(const QPoint &pos, const QString &text, QWidget *w)
 	PopupLabel::_instance->place(pos, w);
 	PopupLabel::_instance->showNormal();
 }
+
+void Popup::clear()
+{
+	if (PopupLabel::_instance)
+		PopupLabel::_instance->deleteLater();
+}

src/GUI/popup.h

@@ -9,6 +9,7 @@ class Popup
 {
 public:
 	static void show(const QPoint &pos, const QString &text, QWidget *w);
+	static void clear();
 };
 
 #endif // POPUP_H