Fixing regression
Fixing regression

* purging draw manager sets graphics device to null

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