citra-qt: Fix connect error on startup

src/citra_qt/bootmanager.cpp

@@ -128,9 +128,6 @@ GRenderWindow::GRenderWindow(QWidget* parent, EmuThread* emu_thread) :
 
     BackupGeometry();
 
-#if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
-    connect(this->windowHandle(), SIGNAL(screenChanged(QScreen*)), this, SLOT(OnFramebufferSizeChanged()));
-#endif
 }
 
 void GRenderWindow::moveContext()
@@ -278,3 +275,12 @@ void GRenderWindow::OnEmulationStarting(EmuThread* emu_thread) {
 void GRenderWindow::OnEmulationStopping() {
     emu_thread = nullptr;
 }
+
+void GRenderWindow::showEvent(QShowEvent * event) {
+    QWidget::showEvent(event);
+
+    // windowHandle() is not initialized until the Window is shown, so we connect it here.
+    #if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
+        connect(this->windowHandle(), SIGNAL(screenChanged(QScreen*)), this, SLOT(OnFramebufferSizeChanged()), Qt::UniqueConnection);
+    #endif
+}

src/citra_qt/bootmanager.h

@@ -123,13 +123,12 @@ public:
 
     void OnClientAreaResized(unsigned width, unsigned height);
 
-    void OnFramebufferSizeChanged();
-
 public slots:
     void moveContext();  // overridden
 
     void OnEmulationStarting(EmuThread* emu_thread);
     void OnEmulationStopping();
+    void OnFramebufferSizeChanged();
 
 signals:
     /// Emitted when the window is closed
@@ -146,4 +145,7 @@ private:
     int keyboard_id;
 
     EmuThread* emu_thread;
+
+protected:
+    void showEvent(QShowEvent* event) override;
 };