fix: validate api occurs an error when there is folded tree row

[jajugoguma]

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Description

• Fixed an issue that is occurring an error when calling validate with folded tree row.
  • The tree row that has never been opened is not observable data. So, view data of it doesn't have any value properties.
  • Because it doesn't have any properties needed for validating, The error occurred.
  • So, before validating, check if there is non-observable row and then change it to an observable row.

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