[FIX] sale: bad error message when invoicing sales order

When trying to invoice undelivered quantities the error message
was somewhat misleading: it indicates as a possible solution a
Stock app feature even when Stock is not installed.

After this commit the message will be more appropriated.

opw - 3206001

closes odoo/odoo#114754

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>