Check date_end in lines before terminate contract
CHANGELOG:
### FIXED
- [#614](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/614) Check if all lines are ended before terminate contract
Related card: https://trello.com/c/6YJ3HgKg/945-error-al-finalitzar-contracte
Edited by Pelayo García