Sortable - prevent placement at the last row
I have a list, with the last item being an "add item" button. I can prevent it from being sortable by setting `cancel: ".btn-add"`, but that doesn't prevent items from being placed *after* the add button.
I could replace the add button at the end of each sorting operation, but the user will still get wrong feedback during sorting.
Is there any way to prevent this, other than creating an extra container for the actual list so that it doesn't contain the add button?