fix unloaded appdomain
fix unloaded appdomain

//stop timer on domain unload, otherwise:
//Exception: System.AppDomainUnloadedException
//Message: Attempted to access an unloaded AppDomain.

fixes #819

littlesmilelove/NLog,RichiCoder1/NLog,nazim9214/NLog,pwelter34/NLog,BrutalCode/NLog,RRUZ/NLog,MoaidHathot/NLog,BrutalCode/NLog,pwelter34/NLog,AndreGleichner/NLog,hubo0831/NLog,rajeshgande/NLog,czema/NLog,FeodorFitsner/NLog,luigiberrettini/NLog,RRUZ/NLog,czema/NLog,czema/NLog,zbrad/NLog,sean-gilliam/NLog,ajayanandgit/NLog,MoaidHathot/NLog,Niklas-Peter/NLog,bjornbouetsmith/NLog,luigiberrettini/NLog,michaeljbaird/NLog,kevindaub/NLog,bhaeussermann/NLog,ie-zero/NLog,MartinTherriault/NLog,tohosnet/NLog,UgurAldanmaz/NLog,Niklas-Peter/NLog,michaeljbaird/NLog,zbrad/NLog,bhaeussermann/NLog,matteobruni/NLog,NLog/NLog,campbeb/NLog,ArsenShnurkov/NLog,AndreGleichner/NLog,FeodorFitsner/NLog,ie-zero/NLog,ilya-g/NLog,tohosnet/NLog,tetrodoxin/NLog,tmusico/NLog,campbeb/NLog,littlesmilelove/NLog,304NotModified/NLog,rajeshgande/NLog,UgurAldanmaz/NLog,bjornbouetsmith/NLog,bryjamus/NLog,snakefoot/NLog,nazim9214/NLog,hubo0831/NLog,bryjamus/NLog,kevindaub/NLog,ilya-g/NLog,vbfox/NLog,vbfox/NLog,RichiCoder1/NLog,breyed/NLog,matteobruni/NLog,ArsenShnurkov/NLog,babymechanic/NLog,babymechanic/NLog,czema/NLog,ajayanandgit/NLog,breyed/NLog,tmusico/NLog,tetrodoxin/NLog,MartinTherriault/NLog