Fix out of bounds cell location searchs in VolumeRendererStructured

`RectilinearLocator::LocateCell` and `UniformLocator::LocateCell` assume
that the point in inside the bounds of the cell set, but may return a
cell location that does not exist, i.e., cell location that is outside
of the bounds of the cell set due to errors from floating point

This fix, given the assumption above, bounds the calculated cell
location to within the cellset by capping the indices to within the
19 jobs for volume-renderer-oob-fix