[Fix]:only partner with is_company True or parent_id False should be display on selecting partner on move line (Maintenance Case:618763)

Steps:
1. Create a move line manually from Accounting > Journal Entries > Journal Items.
2. Select the partner (You can see that all the partners and contacts are visible here),

Expected behavior: 
Only partner with is_company True or Parent with False (For individual partners) should be visible here for partners.

This branch fixes this issue.