OGRLineString::segmentize() : don't set 0 as z for interpolated points, but the z from the previous point (not sure why we don't do interpolation), also try to fix a false positive Coverity 1074362)

git-svn-id: https://svn.osgeo.org/gdal/trunk@26458 f0d54148-0727-0410-94bb-9a71ac55c965