Fixed crash when close main window.

application/mainwindow.cpp

@@ -133,6 +133,12 @@ void MainWindow::showEvent(QShowEvent *evt)
     }
 }
 
+void MainWindow::closeEvent(QCloseEvent *evt)
+{
+    Context::instance().destroy();
+    evt->accept();
+}
+
 void MainWindow::on_actionSettings_triggered()
 {
     SettingsForm *settings = new SettingsForm(this);