DolphinQt: Disable Display Sleep on Windows.

Disables Display Sleeping on Windows on DolphinQt while the game runs,
and re-enables it after the game closes.

Source/Core/DolphinQt/MainWindow.cpp

@@ -138,11 +138,27 @@ void DMainWindow::StartGame(const QString filename)
 	}
 	else
 	{
-		// TODO: Disable screensaver!
+		DisableScreensaver();
 		emit CoreStateChanged(Core::CORE_RUN);
 	}
 }
 
+void DMainWindow::DisableScreensaver()
+{
+#ifdef Q_OS_WIN
+	// Prevents Windows from sleeping or turning off the display
+	SetThreadExecutionState(ES_CONTINUOUS | ES_DISPLAY_REQUIRED);
+#endif
+}
+
+void DMainWindow::EnableScreensaver()
+{
+#ifdef Q_OS_WIN
+	// Allows Windows to sleep and turn off the display
+	SetThreadExecutionState(ES_CONTINUOUS);
+#endif
+}
+
 QString DMainWindow::RequestBootFilename()
 {
 	// If a game is already selected, just return the filename
@@ -263,8 +279,7 @@ bool DMainWindow::Stop()
 	// TODO: Show the author/description dialog here
 
 	BootManager::Stop();
-
-	// TODO: Allow screensaver again
+	EnableScreensaver();
 	// TODO: Restore original window title
 
 	// TODO:

Source/Core/DolphinQt/MainWindow.h

@@ -68,6 +68,9 @@ private:
 	std::unique_ptr<Ui::DMainWindow> m_ui;
 	DGameTracker* m_game_tracker;
 
+	// Misc.
+	void DisableScreensaver();
+	void EnableScreensaver();
 	// Emulation
 	QString RequestBootFilename();
 	QString ShowFileDialog();