add Assert to debug
add Assert to debug

luonaerduo9/ChatKit-OC,Maru-zhang/ChatKit-OC,leancloud/ChatKit-OC,Maru-zhang/ChatKit-OC,Maru-zhang/ChatKit-OC,wizardguy/ChatKit-OC,Maru-zhang/ChatKit-OC,ChenYilong/ChatKit-OC