remove indirection in vertex builder

src/rendering/twn_rects.c

@@ -85,7 +85,7 @@ void render_rect_batch(const Primitive2D primitives[],
             Vec2 v3 = { rect.rect.x + rect.rect.w, rect.rect.y };
 
             push_quad_payload_to_vertex_buffer_builder(
-                batch, &payload,
+                batch, i, &payload,
                 v0, v1, v2, v3,
                 (Vec2){0}, (Vec2){0}, (Vec2){0}, (Vec2){0},
                 rect.color);