Fixed infinite loop when deleting groups/entities

Sledge.Editor/Actions/MapObjects/Operations/CreateEditDelete.cs

@@ -204,11 +204,11 @@ public virtual void Perform(Document document)
             do
             {
                 // Exclude world objects, but we want to remove Group and (brush) Entity objects as they are invalid if empty.
-                emptyParents = objects.Where(x => x.Parent != null && !(x.Parent is World) && x.Parent.Children.All(objects.Contains)).ToList();
+                emptyParents = objects.Where(x => x.Parent != null && !(x.Parent is World) && x.Parent.Children.All(objects.Contains) && !objects.Contains(x.Parent)).ToList();
                 foreach (var ep in emptyParents)
                 {
                     // Add the parent object into the delete list
-                    if (!objects.Contains(ep.Parent)) objects.Add(ep.Parent);
+                    objects.Add(ep.Parent);
                 }
             } while (emptyParents.Any()); // If we changed the collection, we need to re-check