Check Connection.IsLoggedIn.

Make sure the found connection is logged in, otherwise a null `User` will be passed to `ModelServiceFactory` and things break.

Author: grokys

src/GitHub.App/ViewModels/GitHubPane/GitHubPaneViewModel.cs

@@ -370,7 +370,7 @@ async Task UpdateContent(ILocalRepositoryModel repository)
 
                 Connection = await connectionManager.GetConnection(hostAddress);
 
-                if (Connection != null)
+                if (Connection?.IsLoggedIn == true)
                 {
                     navigator.Clear();
                     Content = navigator;