Warn user before closing composer with unset message. Closes #4290
Warn user before closing composer with unset message. Closes #4290

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