Fix NRE from Tilemap Layer
Fix NRE from Tilemap Layer

+ See https://github.com/mono/CocosSharp/issues/101

MSylvia/CocosSharp,TukekeSoft/CocosSharp,zmaruo/CocosSharp,hig-ag/CocosSharp,MSylvia/CocosSharp,hig-ag/CocosSharp,zmaruo/CocosSharp,mono/CocosSharp,haithemaraissia/CocosSharp,haithemaraissia/CocosSharp,TukekeSoft/CocosSharp,mono/CocosSharp