[sale] Sale Calendar Issue

- Task: https://www.odoo.com/web/#id=8411&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.PvjYdFX70QJTQioP
Hello @rim, 
Actually the feature of selection box was not introduced previously thats why they were using -1 for checking the value of filters but now in this branch this feature is introduced and in selection box we will not get filter values as ids of record in selection box its like [('draft': 'DRAFT'), ('done': 'DONE')] and in this case key will be 'draft' and its not an id thats why we had removed -1.
And about the next point of line 2 where they are checking -1 condition that will for the many2one.