Fix loading screen graphical artifacts on window resize

Recreate Vulkan swapchain in LoadingScreen::render() when the dirty flag
is set, so resizing the window during world loading no longer renders
into a stale swapchain with mismatched framebuffers.

src/core/application.cpp

@@ -3065,6 +3065,7 @@ void Application::loadOnlineWorldTerrain(uint32_t mapId, float x, float y, float
     // --- Loading screen for online mode ---
     rendering::LoadingScreen loadingScreen;
     loadingScreen.setVkContext(window->getVkContext());
+    loadingScreen.setSDLWindow(window->getSDLWindow());
     bool loadingScreenOk = loadingScreen.initialize();
 
     auto showProgress = [&](const char* msg, float progress) {