fix(ingest): fix error in newml2 parser when slugline is empty
fix(ingest): fix error in newml2 parser when slugline is empty

it throws `KeyError` an fails to continue ingesting

SD-1435

sivakuna-aap/superdesk,akintolga/superdesk-aap,Aca-jov/superdesk,amagdas/superdesk,vied12/superdesk,sivakuna-aap/superdesk,akintolga/superdesk-aap,plamut/superdesk,ioanpocol/superdesk,petrjasek/superdesk-server,amagdas/superdesk,sjunaid/superdesk,sjunaid/superdesk,amagdas/superdesk,vied12/superdesk,gbbr/superdesk,sivakuna-aap/superdesk,mdhaman/superdesk,fritzSF/superdesk,mdhaman/superdesk-aap,pavlovicnemanja92/superdesk,marwoodandrew/superdesk,vied12/superdesk,marwoodandrew/superdesk,superdesk/superdesk-ntb,mdhaman/superdesk-aap,akintolga/superdesk,gbbr/superdesk,plamut/superdesk,Aca-jov/superdesk,darconny/superdesk,amagdas/superdesk,thnkloud9/superdesk,superdesk/superdesk-aap,marwoodandrew/superdesk-aap,superdesk/superdesk-ntb,marwoodandrew/superdesk-aap,hlmnrmr/superdesk,superdesk/superdesk-aap,pavlovicnemanja/superdesk,fritzSF/superdesk,liveblog/superdesk,ioanpocol/superdesk,verifiedpixel/superdesk,marwoodandrew/superdesk,pavlovicnemanja92/superdesk,petrjasek/superdesk,marwoodandrew/superdesk-aap,superdesk/superdesk-ntb,petrjasek/superdesk-ntb,mdhaman/superdesk,superdesk/superdesk-aap,fritzSF/superdesk,sjunaid/superdesk,petrjasek/superdesk-server,mdhaman/superdesk,petrjasek/superdesk-ntb,marwoodandrew/superdesk,pavlovicnemanja/superdesk,marwoodandrew/superdesk,mugurrus/superdesk,vied12/superdesk,verifiedpixel/superdesk,petrjasek/superdesk,ancafarcas/superdesk,superdesk/superdesk-aap,akintolga/superdesk,hlmnrmr/superdesk,pavlovicnemanja92/superdesk,liveblog/superdesk,superdesk/superdesk-ntb,liveblog/superdesk,superdesk/superdesk,pavlovicnemanja92/superdesk,plamut/superdesk,plamut/superdesk,thnkloud9/superdesk,petrjasek/superdesk,petrjasek/superdesk-ntb,hlmnrmr/superdesk,petrjasek/superdesk-ntb,Aca-jov/superdesk,plamut/superdesk,marwoodandrew/superdesk-aap,ioanpocol/superdesk-ntb,verifiedpixel/superdesk,fritzSF/superdesk,darconny/superdesk,gbbr/superdesk,verifiedpixel/superdesk,superdesk/superdesk,mdhaman/superdesk-aap,mugurrus/superdesk,pavlovicnemanja/superdesk,pavlovicnemanja/superdesk,liveblog/superdesk,thnkloud9/superdesk,sivakuna-aap/superdesk,darconny/superdesk,liveblog/superdesk,ancafarcas/superdesk,ioanpocol/superdesk-ntb,amagdas/superdesk,ioanpocol/superdesk,superdesk/superdesk,akintolga/superdesk,akintolga/superdesk-aap,superdesk/superdesk,ioanpocol/superdesk-ntb,mugurrus/superdesk,ancafarcas/superdesk,petrjasek/superdesk,akintolga/superdesk,pavlovicnemanja92/superdesk,fritzSF/superdesk,sivakuna-aap/superdesk,mdhaman/superdesk-aap,vied12/superdesk,verifiedpixel/superdesk,akintolga/superdesk,akintolga/superdesk-aap