BUG: Fix bounds computation in vtkMultiVolume

This line set the homogeneous IJK coordinates incorrectly:

    pointsDataCoords.emplace_back(bounds[1], bounds[3], bounds[5], 0.);

The problem is that the last component is set to 0 instead of 1
(the coordinates specify a direction vector and not a position).
When this vector is multiplied by the homogeneous transformation matrix,
the position is incorrect, because the translation component of the matrix
is not taken into account.

fixes https://github.com/Slicer/Slicer/issues/8301
fixes #19447

Rendering/Volume/vtkMultiVolume.cxx

@@ -214,7 +214,7 @@ std::array<double, 6> vtkMultiVolume::ComputeAABounds(double bounds[6], vtkMatri
   pointsDataCoords.emplace_back(minPoint + Point(0., dim[1], 0., 0.));
   pointsDataCoords.emplace_back(minPoint + Point(0., 0., dim[2], 0.));
   pointsDataCoords.emplace_back(minPoint + Point(dim[0], 0., dim[2], 0.));
-  pointsDataCoords.emplace_back(bounds[1], bounds[3], bounds[5], 0.);
+  pointsDataCoords.emplace_back(minPoint + Point(dim[0], dim[1], dim[2], 0.));
   pointsDataCoords.emplace_back(minPoint + Point(0., dim[1], dim[2], 0.));
 
   // Transform all points from data to world coordinates