`ContourSpatialObject<TDimension>::Update()` LINEAR_INTERPOLATION case may need some adjustment

There is a line of code in `ContourSpatialObject::Update()` that looks suspicious to me:

newPoint = pnt[d] + i * step[d];

https://github.com/InsightSoftwareConsortium/ITK/blob/a2b39155dae42fb88d52c0d7d7d7e1f1a8c3e954/Modules/Core/SpatialObjects/include/itkContourSpatialObject.hxx#L217-L225

You see, `newPoint` is a `PointType`, and it gets filled by a scalar value, `pnt[d] + i * step[d]`, over and over again, inside the inner for loop.

I think the intention was to do:

newPoint[d] = pnt[d] + i * step[d];

But I'm not sure, because I did not study the code well enough yet! Any feedback or possible explanation is welcome!

_Note: This bug report is still in progress! More details soon, hopefully!_