qt: Show the window only once the page is fully loaded

The application prints the cookie and exits almost immediately if
there is already a valid session, thus causing the window to flicker.
To prevent that, we now wait for the page to be fully loaded before
showing the window.

openfortivpn-webview-qt/main.cpp

@@ -95,7 +95,6 @@ int main(int argc, char *argv[])
     w.loadUrl(url);
     w.resize(1024, 760);
     w.move(findScreenWithCursor()->geometry().center() - w.rect().center());
-    w.show();
 
     return app.exec();
 }

openfortivpn-webview-qt/mainwindow.cpp

@@ -50,6 +50,10 @@ MainWindow::MainWindow(const bool keepOpen,
             &MainWindow::onCookieRemoved);
 
     connect(webEnginePage, &QWebEnginePage::certificateError, this, &MainWindow::onCertificateError);
+
+    // Show the window only once the page is fully loaded. In this way we won't even show it if the
+    // cookie is available immediately because of some existing session.
+    connect(webEnginePage, &QWebEnginePage::loadFinished, this, [this] { show(); }, Qt::SingleShotConnection);
 }
 
 MainWindow::~MainWindow()