Deleting an invoice line related to a sale does not reinvoice them
Steps to reproduce:
1. Create a sale with one lines and process it
2. Open the related invoice and delete one of lines
3. Reload the sale and there is no invoice related.
Expected behaviour:
There is one line still pending to invoice and the only way to remove it is to cancel on a related invoice.
Note that the invoice will be created when the shipments are processed, but if all the shipments of this sale are processed the invoice line will be never recreated as the sale won't be processed anymore (there are no related invoices as the lines have been deleted).