Don't load tab multiple times at once

Author: jcansdale

src/GitHub.App/ViewModels/Dialog/Clone/RepositorySelectViewModel.cs

@@ -129,7 +129,7 @@ static string GroupName(KeyValuePair<string, IReadOnlyList<RepositoryListItemMod
 
         async Task LoadItems(bool refresh)
         {
-            if (connection == null && !IsLoading) return;
+            if (connection == null || IsLoading) return;
 
             Error = null;
             IsLoading = true;