`CellUnionFromIntersection` calls `Normalize()`

[missinglink]

Both the CPP and Go versions of CellUnionFromIntersection state that the intersection algo produces a result that is in sorted order.

The go code calls cu.Normalize() anyway, what is the purpose of this?

geo/s2/cellunion.go

Lines 107 to 108 in 6adc566

	// The output is generated in sorted order.
	cu.Normalize()

The CPP code doesn't call normalize:

https://github.com/google/s2geometry/blob/0fb1b8a1474f3137c8b44a7861e31f8efd1370e2/src/s2/s2cell_union.cc#L376

[missinglink]

https://github.com/google/s2geometry/blob/0fb1b8a1474f3137c8b44a7861e31f8efd1370e2/src/s2/s2cell_union.cc#L371

[jmr]

@rsned