Added record has wrong WBS

[bmblb]

Reported by client.
Steps to reproduce on basic gantt demo:

1. disable autoLoad
2. load this data

gantt.project.loadInlineData({
    eventsData : [
        {
            id                 : '71114',
            orderedParentIndex : 0,
            duration           : 1,
            durationUnit       : 'day',
            cls                : '',
            name               : 'a',
            manuallyScheduled  : false,
            unscheduled        : false,
            percentDone        : 0,
            effortUnit         : 'hour',
            effortDriven       : false,
            schedulingMode     : 'Normal',
            baselines          : [],
            wbsValue           : '1'
        },
        {
            id                 : '71116',
            orderedParentIndex : 1,
            duration           : 1,
            durationUnit       : 'day',
            cls                : '',
            name               : 'c',
            manuallyScheduled  : false,
            unscheduled        : false,
            percentDone        : 0,
            effortUnit         : 'hour',
            effortDriven       : false,
            schedulingMode     : 'Normal',
            baselines          : [],
            wbsValue           : '2'
        },
        {
            id                 : '71115',
            orderedParentIndex : 2,
            duration           : 1,
            durationUnit       : 'day',
            cls                : '',
            name               : 'b',
            manuallyScheduled  : false,
            unscheduled        : false,
            percentDone        : 0,
            effortUnit         : 'hour',
            effortDriven       : false,
            schedulingMode     : 'Normal',
            baselines          : [],
            wbsValue           : '3'
        }
    ],
    resourcesData    : [],
    dependenciesData : [],
    assignmentsData  : []
});

3. create a function to apply changes

window.run = function() {
    gantt.project.applyProjectChanges({
        tasks : {
            added : [
                {
                    $PhantomId         : '_generatedModelClass_dd9103c2-b2ff-440a-b5f2-9966687b59ca',
                    cls                : '',
                    duration           : 1,
                    durationUnit       : 'day',
                    effortDriven       : false,
                    effortUnit         : 'hour',
                    id                 : 71117,
                    manuallyScheduled  : false,
                    name               : 'New task 3',
                    orderedParentIndex : 2,
                    percentDone        : 0,
                    schedulingMode     : 'Normal',
                    unscheduled        : false,
                    wbsValue           : '3'
                }
            ],
            updated : [
                {
                    id                 : '71115',
                    orderedParentIndex : 3,
                    wbsValue           : '4'
                }
            ]
        }
    });
};

4. load demo, type run() in console

You'll see new task WBS is 4, it should be 3.