Fix SEGV on ESC in chart settings

If you press ESC on the chart settings (not add chart) dialog
then the dialog is closed and deleted, causing a SEGV. This
patch overrides reject() to ensure the dialog is just hidden.

src/ChartSettings.cpp

@@ -60,3 +60,9 @@ ChartSettings::closeEvent(QCloseEvent* event)
     event->ignore();
     hide();
 }
+
+void
+ChartSettings::reject()
+{
+    hide();
+}

src/ChartSettings.h

@@ -34,6 +34,9 @@ class ChartSettings : public QDialog
         ChartSettings(QWidget *parent, QWidget *contents);
         void closeEvent(QCloseEvent* event);
 
+    public slots:
+        void reject();
+
     private:
         QPushButton *btnOK;