Add missing Close() statement

SimpleHttpServer/HttpServer.cs

@@ -279,6 +279,9 @@ public sealed class HttpServer {
             await HandleDefaultErrorPageAsync(rc, 500);
             mainLogger.Fatal($"Caught otherwise uncaught exception while ProcessingRequest:\n{ex}");
         }
+        finally {
+            rc.ListenerContext.Response.Close();
+        }
 
         LogRequest();
     }