Project direction set to null after changing to Forward

[bmblb]

Reported here: https://forum.bryntum.com/viewtopic.php?f=52&t=30409&p=154459#p154459

To reproduce on advanced demo add two buttons with these two handlers and toggle modes.

onSetDirectionForward() {
    const { gantt } = this;

    console.log("Direction before change to forward: ", gantt.project.direction);

    gantt.project.direction = 'Forward';

    gantt.project.startDate = new Date();
    gantt.project.endDate = null;

    gantt.project.commitAsync().then(_ => {
        console.log("Direction after change to forward: ", gantt.project.direction);
    })
}

onSetDirectionBackward() {
    const { gantt } = this;

    console.log("Direction before change to backward: ", gantt.project.direction);

    gantt.project.direction = 'Backward';

    gantt.project.commitAsync().then(_ => {
        console.log("Direction after change to backward: ", gantt.project.direction);
    })
}