qt: Restore Close button on monitor windows

src/qt/qt_mainwindow.cpp

@@ -583,7 +583,7 @@ void MainWindow::initRendererMonitorSlot(int monitor_index)
         {
             this->renderers[monitor_index]->show();
         });
-        secondaryRenderer->setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowTitleHint);
+        secondaryRenderer->setWindowFlags(Qt::CustomizeWindowHint | Qt::WindowTitleHint | Qt::WindowCloseButtonHint);
         secondaryRenderer->setWindowTitle(QObject::tr("86Box Monitor #") + QString::number(monitor_index + 1));
 
         if (vid_resize == 2) {

src/qt/qt_rendererstack.cpp

@@ -443,3 +443,10 @@ RendererStack::blitCommon(int x, int y, int w, int h)
     emit blitToRenderer(currentBuf, sx, sy, sw, sh);
     currentBuf = (currentBuf + 1) % imagebufs.size();
 }
+
+void RendererStack::closeEvent(QCloseEvent* event)
+{
+    event->ignore();
+    main_window->close();
+}
+

src/qt/qt_rendererstack.hpp

@@ -31,6 +31,7 @@ public:
     void mouseMoveEvent(QMouseEvent *event) override;
     void wheelEvent(QWheelEvent *event) override;
     void leaveEvent(QEvent *event) override;
+    void closeEvent(QCloseEvent *event) override;
     void keyPressEvent(QKeyEvent *event) override
     {
         event->ignore();