support MI_MAX_COUNT in ShaderGen

inc/hgl/graph/mtl/StdMaterial.h

@@ -4,3 +4,13 @@
 #define STD_MTL_NAMESPACE_END   }}}
 
 #define STD_MTL_NAMESPACE_USING using namespace hgl::graph::mtl;
+
+namespace hgl
+{
+    namespace graph
+    {
+        namespace mtl
+        {
+        }//namespace mtl
+    }//namespace graph
+}//namespace hgl