Add IShaderConstantSetCallBack::OnCreate to allow earlier access to IMaterialRendererServices

Accessing IMaterialRendererServices outside of OnSetConstants can be useful and Irrlicht made this a bit too hard to access.
Also OnCreate allows actually for nicer code where initialization and update of shader constants are strictly separated (see changed example).

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6465 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/CD3D9Driver.cpp

@@ -3176,6 +3176,10 @@ s32 CD3D9Driver::addShaderMaterial(const c8* vertexShaderProgram,
 		callback, getMaterialRenderer(baseMaterial), userData);
 
 	r->drop();
+
+	if (callback && nr >= 0)
+		callback->OnCreate(this, userData);
+
 	return nr;
 }
 
@@ -3213,6 +3217,9 @@ s32 CD3D9Driver::addHighLevelShaderMaterial(
 
 	r->drop();
 
+	if (callback && nr >= 0)
+		callback->OnCreate(r, userData);
+
 	return nr;
 }