[12.0][BUG] fieldservice_account, total_cost raise error by some employee in timesheet

[kittiu]

During writing test script I found following error when print order.total_cost

  File "/home/kittiu/ecosoft-odoo/field-service/fieldservice_account/models/fsm_order.py", line 52, in _compute_total_cost
    order.total_cost += line.unit_amount * rate
UnboundLocalError: local variable 'rate' referenced before assignment

Currently, we don't see the error on Work Order screen because,

1. User may choose the employee with user_id, AND
2. field "total_cost" is not show in the view, and so the method _compute_total_cost() is not called.

Steps to Error

1. First, we need to modify view fieldservice_account.fsm_order_form_accounting to also show total_cost
2. Create new Work Order, and select employee that has no user_id, i.e., Abigail Peterson
3. Save it, and you will see the error.