getMaterialCount in custom node example was non-const, reported by vitek

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1163 dfc29bdd-3216-0410-991c-e03cc46cb475

examples/03.CustomSceneNode/main.cpp

@@ -137,7 +137,7 @@ public:
 		return Box;
 	}
 
-	virtual u32 getMaterialCount()
+	virtual u32 getMaterialCount() const
 	{
 		return 1;
 	}