Gantt Charts: TypeError: Cannot read property ‘id’ of undefined in _dragMove when dragging tasks with percentComplete

[AsifMahmoodR]

Overview:
When using the Gantt chart’s built‑in drag/resize (via allowDrag: "1"), charts with tasks that include both an id and percentComplete property throw following error when drag begins:

Steps to Reproduce:

1. I have replicated the issue using one of JSFiddle from FusionCharts Gantt documentation: https://jsfiddle.net/75y2kp9b/
2. The first two tasks are configured with percentComplete.
3. Open browser console and attempt to drag any of the first two tasks, you should see the above error.
4. Attempt to drag any other tasks, works as expected.

fusioncharts Version: 4.1.2

Expected Behavior
Dragging a bar (resize or move) should never throw an error and should perform as expected.