Fix zIndex handling for unmanaged layers

rendering/cases/multiple-layers/main.js

@@ -4,8 +4,10 @@ import {Vector as VectorLayer, Tile as TileLayer} from '../../../src/ol/layer.js
 import {Vector as VectorSource, XYZ} from '../../../src/ol/source.js';
 import GeoJSON from '../../../src/ol/format/GeoJSON.js';
 import {Style, Stroke} from '../../../src/ol/style.js';
+import Feature from '../../../src/ol/Feature.js';
+import Point from '../../../src/ol/geom/Point.js';
 
-new Map({
+const map = new Map({
   layers: [
     new TileLayer({
       source: new XYZ({
@@ -14,6 +16,7 @@ new Map({
       })
     }),
     new VectorLayer({
+      zIndex: 1,
       style: new Style({
         stroke: new Stroke({
           color: 'rgba(255,255,255,0.5)',
@@ -33,4 +36,11 @@ new Map({
   })
 });
 
+const unmanaged = new VectorLayer({
+  source: new VectorSource({
+    features: [new Feature(new Point([0, 0]))]
+  })
+});
+unmanaged.setMap(map);
+
 render();