Not attribute total_seconds() when run sqlite tests and cost is 0 (int)
Running tests with Sqlite and project_revenue installed:
File "/home/resteve/virtualenv/xxx/trytond/trytond/modules/project_revenue/work.py", line 83, in _get_cost
cost = cost.total_seconds()
AttributeError: 'int' object has no attribute 'total_seconds'
because cost value is 0 (int) and only check when is a float [1] to do total_seconds()
[1] https://bitbucket.org/tryton/project_revenue/src/beebbf1b57f450146f0ee602409707c06d358905/work.py?at=default&fileviewer=file-view-default#work.py-82