Clear scene on error on load

agui2/src/MainWindow.cpp

@@ -212,6 +212,8 @@ void MainWindow::on_actionOpen_triggered() {
     }
     catch (const std::exception& e) {
         QMessageBox::critical(this, "Error", e.what());
+        this->scene->clear();
+        this->outputBox = nullptr;
     }
 }