Before this commit, when only planning app is installed and the user goes to Planning > Schedule > By Role, a traceback is raised because the resource_id is not found inside work intervals fetched. The reason is because `this.row.resId` is the resource id only if the first group is resource_id and not something else and so when the group by is `role_id > resource_id` the `resId` will return the role id and not the resource id. It would mean the compute work hours should not be done when the group by does not start by resource.

This commit avoids computing the work hours when the progressField is not a employee, that is, when the group by does not start by resource_id.

Affected version(s): master

Steps to reproduce the issue:
============================
1. Install planning app
2. Go to planning > Schedule > By Role

Current Behavior:
================
A traceback is occured because a role id is not found inside work intervals per resource id.

Expected Behavior:
=================
The Gantt view should be loaded without any issue.

runbot-61438

X-original-commit: 5831c225