notify user if email parsing failed

mainwindow.cpp

@@ -175,6 +175,15 @@ void MainWindow::on_parse_email_button_clicked() {
     EmailParser email_parser;
     std::map<std::string, std::string> paramsMap = email_parser.parse_file(filename.toStdString());
 
+    if (paramsMap.empty()) {
+        QMessageBox infoDialog;
+        infoDialog.setText(tr("QR code in this E-Mail was not found. If you are sure that the e-mail you supplied has qr code, please, contact the developer and send him the .eml file."));
+        infoDialog.setIcon(QMessageBox::Critical);
+        infoDialog.setWindowTitle(tr("QR code was not found in E-Mail"));
+        infoDialog.exec();
+        return;
+    }
+
     set_check_params(paramsMap);
     // QMessageBox infoDialog;
     // infoDialog.setText(tr("This feature is under development. Wait it to appear in next updates."));