Fix: Function to find last invoice must look only into number

htdocs/langs/en_US/bills.lang

@@ -3,13 +3,16 @@ CHARSET=UTF-8
 Bill=Invoice
 Bills=Invoices
 BillsCustomers=Customer's invoices
+BillsCustomer=Customer's invoice
 BillsSuppliers=Supplier's invoices
 BillsCustomersUnpaid=Unpaid customer's invoices
 BillsCustomersUnpaidForCompany=Unpaid customer's invoices for %s
 BillsSuppliersUnpaid=Unpaid supplier's invoices
 BillsUnpaid=Unpaid
+BillsLate=Late payments
 BillsStatistics=Customer's invoices statistics
 BillsStatisticsSuppliers=Supplier's invoices statistics
+DisabledBecauseNotErasable=Disabled because can not be erased
 InvoiceStandard=Standard invoice
 InvoiceStandardAsk=Standard invoice
 InvoiceStandardDesc=This kind of invoice is the common invoice.