fix unexpected close when launch external app (#2617)

* fix unexpected close when launch external app

* update

src/core/flameshot.cpp

@@ -411,6 +411,12 @@ void Flameshot::exportCapture(QPixmap capture,
     if (!(tasks & CR::UPLOAD)) {
         emit captureTaken(capture);
     }
+    // hacks: close a window to trigger qt's quitOnLastWindowClose
+    // if not create tmp_window and close, the `flameshot gui` won't exit after
+    // click copy button
+    QWidget* tmp = new QWidget();
+    tmp->show();
+    tmp->close();
 }
 
 // STATIC ATTRIBUTES