[Fix] (MG_State/Texture): revert GetUnpackParam_ to private

MG/MG_GL/State/Texture/TextureState.h

@@ -62,8 +62,8 @@ private:
     std::vector<GLuint> freeID_;
 
     MG_Global::unordered_map<GLenum, TextureObject> proxyTextures_;
-    
     static GLint GetUnpackParam_(GLenum pname);
+
 public:
     TextureState();
     
@@ -71,6 +71,7 @@ public:
     bool IsTexture(GLuint texture);
     MG_Global::unordered_map<GLuint, TextureObject> textures;
 
+
     // Return: the validity of the operation, according to OpenGL 3 standard
     GLenum BindUnit(GLenum textureUnit);
     GLenum Create(GLuint* texture);