Wait this.referenceSpace to be set before calling this.initLayer (#5626)

Author: vincentfretin

src/components/layer.js

@@ -212,6 +212,7 @@ module.exports.Component = registerComponent('layer', {
 
   tick: function () {
     if (!this.el.sceneEl.xrSession) { return; }
+    if (!this.referenceSpace) { return; }
     if (!this.layer && (this.el.sceneEl.is('vr-mode') || this.el.sceneEl.is('ar-mode'))) { this.initLayer(); }
     this.updateTransform();
     if (this.data.src.complete && (this.pendingCubeMapUpdate || this.loadingScreen || this.visibilityChanged)) { this.loadCubeMapImages(); }