ExtJS wrapper class in extjsmodern demo crashes

[arcady-zherdev]

Reported here: https://forum.bryntum.com/viewtopic.php?f=49&t=25842&p=132103

Steps to reproduce:

1. open Gantt extjsmodern demo
2. run this code in console

dlg = new Ext.Dialog({
    height: 500,
    width: 500,
    layout: 'fit',
    items: [{
        title: 'Bryntum Gantt',
        rtl,
        xtype: 'ganttpanel',
        flex: 1,
        startDate: new Date(2019, 0, 6),
        project: new bryntum.gantt.ProjectModel({
            autoLoad: true,
            loadUrl: '../_datasets/launch-saas.json'
        }),
        header: {
            items: [{
                xtype: 'spinnerfield',
                label: 'Row height',
                width: '12.5em',
                bind: '{rh}',
                minValue: 20
            }, {
                xtype: 'button',
                iconCls: 'b-fa b-fa-plus',
                text: 'Add Task',
                ui: 'action',
                handler: 'addTask',
                cls: 'b-add-task'
            }]
        },

        viewModel: {
            data: {
                rh: 35
            }
        },
        bind: {
            rowHeight: '{rh}'
        },

        features: {
            taskMenu: {
                // Our items is merged with the provided defaultItems
                // So we add the provided convertToMilestone option.
                items: {
                    convertToMilestone: true
                },
                processItems({ taskRecord, items }) {
                    if (taskRecord.isMilestone) {
                        items.convertToMilestone = false;
                    }
                }
            },
            filter: true,
            dependencyEdit: true,
            timeRanges: {
                showCurrentTimeLine: true
            },
            labels: {
                left: {
                    field: 'name',
                    editor: {
                        type: 'textfield'
                    }
                }
            }
        },

        columns: [
            { type: 'wbs' },
            { type: 'name', width: 250 },
            { type: 'startdate' },
            { type: 'duration' },
            { type: 'percentdone', width: 70 },
            {
                type: 'successor',
                width: 112
            },
            { type: 'schedulingmodecolumn' },
            { type: 'calendar' },
            { type: 'constrainttype' },
            { type: 'constraintdate' },
            {
                type: 'date',
                text: 'Deadline',
                field: 'deadline'
            },
            { type: 'addnew' }
        ]
    }]
}).show()