Fix startup message

Jellyfin.Server/Middleware/ServerStartupMessageMiddleware.cs

@@ -1,5 +1,6 @@
 using System.Net.Mime;
 using System.Threading.Tasks;
+using MediaBrowser.Controller;
 using MediaBrowser.Model.Globalization;
 using Microsoft.AspNetCore.Http;
 
@@ -25,10 +26,20 @@ namespace Jellyfin.Server.Middleware
         /// Executes the middleware action.
         /// </summary>
         /// <param name="httpContext">The current HTTP context.</param>
+        /// <param name="serverApplicationHost">The server application host.</param>
         /// <param name="localizationManager">The localization manager.</param>
         /// <returns>The async task.</returns>
-        public async Task Invoke(HttpContext httpContext, ILocalizationManager localizationManager)
+        public async Task Invoke(
+            HttpContext httpContext,
+            IServerApplicationHost serverApplicationHost,
+            ILocalizationManager localizationManager)
         {
+            if (serverApplicationHost.CoreStartupHasCompleted)
+            {
+                await _next(httpContext).ConfigureAwait(false);
+                return;
+            }
+
             var message = localizationManager.GetLocalizedString("StartupEmbyServerIsLoading");
             httpContext.Response.StatusCode = StatusCodes.Status503ServiceUnavailable;
             httpContext.Response.ContentType = MediaTypeNames.Text.Html;