Fix assertion when folder null; fix #6574
Fix assertion when folder null; fix #6574

jimbonator/geary,kyoushuu/geary,martinra/geary,tshikaboom/geary,emersion/geary,AtticHacker/geary,githubnemo/geary,robol/geary,mjog/geary,robol/geary,rschroll/geary,rschroll/geary,jimbonator/geary,glebihan/geary,jimbonator/geary,emersion/geary,geekvigilante/geary,mjog/geary,aatishnn/geary,mpdeimos/geary,glebihan/geary,tshikaboom/geary,AtticHacker/geary,kyoushuu/geary,tshikaboom/geary,kpiwko/geary,MohamedIM/geary-unofficial,aatishnn/geary,abn/geary,emersion/geary,martinra/geary,martinra/geary,robol/geary,githubnemo/geary,glebihan/geary,aatishnn/geary,AtticHacker/geary,mjog/geary,githubnemo/geary