fix PandasDataFrameObject truthiness

[abyesilyurt]

Description

ObjectDiff[PandasDataFrameObject].non_empty_object property returns the following error without the fix: Truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()

	@property
	def non_empty_object(self) -> SyftObject | None:
        return self.low_obj or self.high_obj

Affected Dependencies

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