SDL: handle SDL_QUIT event

Using SDL_INIT_JOYSTICK implies SDL_INIT_EVENTS which installs a signal
handler for SIGINT and SIGTERM. There will be a way to prevent this in
2.0.4 but for now we'll need to handle SDL_QUIT.

Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp

@@ -134,6 +134,11 @@ void ControllerInterface::Shutdown()
 //
 void ControllerInterface::UpdateInput()
 {
+#ifdef CIFACE_USE_SDL
+	// SDL currently also handles SIGINT and SIGTERM,
+	// so make sure to update it even if there is no SDL device.
+	ciface::SDL::UpdateInput();
+#endif
 	for (ciface::Core::Device* d : m_devices)
 		d->UpdateInput();
 }