avoid negative indicies access to `parenStack` - thanks @talaj! (ref #4096)
avoid negative indicies access to `parenStack` - thanks @talaj! (ref #4096)

naturalatlas/mapnik,lightmare/mapnik,tomhughes/mapnik,mapnik/mapnik,mapnik/mapnik,lightmare/mapnik,mapnik/mapnik,naturalatlas/mapnik,lightmare/mapnik,lightmare/mapnik,naturalatlas/mapnik,tomhughes/mapnik,tomhughes/mapnik,naturalatlas/mapnik,tomhughes/mapnik,mapnik/mapnik