allow empty comment on task, if it has attachment
allow empty comment on task, if it has attachment

irfanah/teambox,codeforeurope/samenspel,crewmate/crewmate,vveliev/teambox,irfanah/teambox,rahouldatta/teambox,teambox/teambox,irfanah/teambox,nfredrik/teambox,nfredrik/teambox,nfredrik/teambox,wesbillman/projects,crewmate/crewmate,ccarruitero/teambox,crewmate/crewmate,rahouldatta/teambox,ccarruitero/teambox,teambox/teambox,vveliev/teambox,teambox/teambox,codeforeurope/samenspel,nfredrik/teambox,alx/teambox,alx/teambox,wesbillman/projects,vveliev/teambox,irfanah/teambox,rahouldatta/teambox,vveliev/teambox