postgis: for an empty table (with null results for extent) return early rather than allowing and printing a lexical cast failure
postgis: for an empty table (with null results for extent) return early rather than allowing and printing a lexical cast failure

lightmare/mapnik,tomhughes/mapnik,whuaegeanse/mapnik,pnorman/mapnik,mapnik/python-mapnik,CartoDB/mapnik,mapnik/mapnik,Uli1/mapnik,yiqingj/work,Uli1/mapnik,mapycz/mapnik,Mappy/mapnik,mbrukman/mapnik,mbrukman/mapnik,tomhughes/python-mapnik,tomhughes/mapnik,rouault/mapnik,whuaegeanse/mapnik,Mappy/mapnik,Uli1/mapnik,tomhughes/mapnik,pramsey/mapnik,whuaegeanse/mapnik,jwomeara/mapnik,kapouer/mapnik,Mappy/mapnik,jwomeara/mapnik,yiqingj/work,davenquinn/python-mapnik,sebastic/python-mapnik,sebastic/python-mapnik,kapouer/mapnik,Airphrame/mapnik,naturalatlas/mapnik,tomhughes/python-mapnik,qianwenming/mapnik,pnorman/mapnik,strk/mapnik,manz/python-mapnik,tomhughes/mapnik,mapnik/python-mapnik,sebastic/python-mapnik,zerebubuth/mapnik,stefanklug/mapnik,mapnik/mapnik,pramsey/mapnik,qianwenming/mapnik,pnorman/mapnik,jwomeara/mapnik,cjmayo/mapnik,manz/python-mapnik,manz/python-mapnik,garnertb/python-mapnik,CartoDB/mapnik,rouault/mapnik,cjmayo/mapnik,mbrukman/mapnik,qianwenming/mapnik,mapnik/mapnik,strk/mapnik,yiqingj/work,stefanklug/mapnik,Mappy/mapnik,kapouer/mapnik,pramsey/mapnik,whuaegeanse/mapnik,yohanboniface/python-mapnik,tomhughes/python-mapnik,mapycz/mapnik,Airphrame/mapnik,naturalatlas/mapnik,garnertb/python-mapnik,qianwenming/mapnik,davenquinn/python-mapnik,mbrukman/mapnik,jwomeara/mapnik,naturalatlas/mapnik,CartoDB/mapnik,strk/mapnik,strk/mapnik,mapycz/python-mapnik,zerebubuth/mapnik,mapycz/mapnik,Uli1/mapnik,stefanklug/mapnik,qianwenming/mapnik,mapycz/python-mapnik,pnorman/mapnik,cjmayo/mapnik,pramsey/mapnik,rouault/mapnik,yohanboniface/python-mapnik,garnertb/python-mapnik,cjmayo/mapnik,Airphrame/mapnik,mapnik/mapnik,lightmare/mapnik,stefanklug/mapnik,zerebubuth/mapnik,yohanboniface/python-mapnik,kapouer/mapnik,yiqingj/work,rouault/mapnik,mapnik/python-mapnik,lightmare/mapnik,naturalatlas/mapnik,lightmare/mapnik,Airphrame/mapnik,davenquinn/python-mapnik