[FIX] project: fix crash when no language selected

Reproduce the issue

    - Select a language (done by default)
    - Install Project
    - Create a project
    - Create a task with a formatted date
    - Reset the language
    - Go on the project

    Traceback

Cause

    In 7e42c663, I format the date_deadline based on the user's language
    but did'nt know that we could have no language selected.

This commit uses the `format_date` method from `odoo.tools.misc`
which fallback on the first language installed if there is no
language selected.

OPW-2146479

closes odoo/odoo#41057

X-original-commit: 7d061357
Signed-off-by: Jason Van Malder <jasonvanmalder@users.noreply.github.com>