[FIX] resource_multi_week_work_time_from_contracts: Handle case where there is no calendar

[carmenbianca]

Description

The upstream get_calendar_for_date can return None. We should respect that.

Odoo task (if applicable)

Checklist before approval

• [ ] Tests are present (or not needed).
• [ ] Credits/copyright have been changed correctly.
• [ ] Change log snippet is present.
• [ ] (If a new module) Moving this to OCA has been considered.

[huguesdk]

/ocabot merge patch

[github-grap-bot]

Hey, thanks for contributing! Proceeding to merge this for you. Prepared branch 12.0-ocabot-merge-pr-329-by-huguesdk-bump-patch, awaiting test results.

[github-grap-bot]

Congratulations, your PR was merged at ca476c119fc27cc45d3cd32202ffcbdeae3a8c69. Thanks a lot for contributing to coopiteasy. ❤️