Fix build with no hexer.
Fix build with no hexer.

lucadelu/PDAL,Sciumo/PDAL,jwomeara/PDAL,jwomeara/PDAL,jwomeara/PDAL,boundlessgeo/PDAL,mtCarto/PDAL,DougFirErickson/PDAL,Sciumo/PDAL,mpgerlek/PDAL-old,Sciumo/PDAL,radiantbluetechnologies/PDAL,radiantbluetechnologies/PDAL,mtCarto/PDAL,jwomeara/PDAL,lucadelu/PDAL,mpgerlek/PDAL-old,mtCarto/PDAL,DougFirErickson/PDAL,lucadelu/PDAL,radiantbluetechnologies/PDAL,DougFirErickson/PDAL,Sciumo/PDAL,boundlessgeo/PDAL,boundlessgeo/PDAL,DougFirErickson/PDAL,mpgerlek/PDAL-old,boundlessgeo/PDAL,radiantbluetechnologies/PDAL,mpgerlek/PDAL-old,lucadelu/PDAL,mtCarto/PDAL