Fix logic.

Don't to try to create an `IModelService` for a non-logged-in connection.

Author: grokys

src/GitHub.Exports.Reactive/Extensions/ConnectionManagerExtensions.cs

@@ -14,7 +14,7 @@ public static async Task<IModelService> GetModelService(
             IModelServiceFactory factory)
         {
             var connection = await cm.GetConnection(repository);
-            return connection != null ? await factory.CreateAsync(connection) : null;
+            return connection?.IsLoggedIn == true ? await factory.CreateAsync(connection) : null;
         }
     }
 }