Collapse state is incorrect when exporting TreeList while some nodes are collapsed.

• https://dojo.telerik.com/@pmilchev/aMUniceC 

Reproduction steps: 

• Open and run the dojo example
• Click the Export button in TreeList
• Click the toggle button of the item

Actual: Alert shows "Collapsed"

Expected: Alert shows "Expanded"

Regression introduced in 2019.2.514
Related to: https://github.com/telerik/kendo-ui-core/issues/4696 

Code: https://github.com/telerik/kendo/blame/master/src/excel/main.js#L43