Don't use fps_max_unfocused for server step time on non-singleplayer …

…main-menu-hosted servers

It's unreasonable to change server step time when the hosting user unfocuses their window.
(m_is_paused is already not set if it's not singleplayer.)

src/client/game.cpp

@@ -2504,7 +2504,7 @@ inline void Game::step(f32 dtime)
 	ZoneScoped;
 
 	if (server) {
-		float fps_max = !device->isWindowFocused() ?
+		float fps_max = !device->isWindowFocused() && simple_singleplayer_mode ?
 				g_settings->getFloat("fps_max_unfocused") :
 				g_settings->getFloat("fps_max");
 		fps_max = std::max(fps_max, 1.0f);