When a text buffer does not represent a document from a workspace...

When a text buffer does not represent a document from a workspace GetOpenDocumentInCurrentContextWithChanges() will return null. Allow for that without a NullReferenceException.

Fixes #24625.

src/EditorFeatures/Core.Wpf/Suggestions/SuggestedActionsSource.cs

@@ -897,6 +897,11 @@ public async Task<ISuggestedActionCategorySet> GetSuggestedActionCategoriesAsync
                 using (var asyncToken = _owner.OperationListener.BeginAsyncOperation(nameof(GetSuggestedActionCategoriesAsync)))
                 {
                     var document = range.Snapshot.GetOpenDocumentInCurrentContextWithChanges();
+                    if (document == null)
+                    {
+                        return null;
+                    }
+
                     using (var linkedTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken))
                     {
                         var linkedToken = linkedTokenSource.Token;