fix #2265 (FallbackGroup could lose log events)
fix #2265 (FallbackGroup could lose log events)

ie-zero/NLog,UgurAldanmaz/NLog,hubo0831/NLog,304NotModified/NLog,luigiberrettini/NLog,luigiberrettini/NLog,BrutalCode/NLog,ie-zero/NLog,snakefoot/NLog,UgurAldanmaz/NLog,nazim9214/NLog,BrutalCode/NLog,sean-gilliam/NLog,NLog/NLog,hubo0831/NLog,nazim9214/NLog