Start the light probe only when xr.getSession returns a not null sess…

…ion, update the VR environment only when a light probe was set up in the first place

src/components/scene/reflection.js

@@ -45,7 +45,7 @@ module.exports.Component = register('reflection', {
       var renderer = self.el.renderer;
       var session = renderer.xr.getSession();
       if (
-        session.requestLightProbe && self.el.is('ar-mode')
+        session && session.requestLightProbe && self.el.is('ar-mode')
       ) {
         self.startLightProbe();
       }
@@ -61,9 +61,9 @@ module.exports.Component = register('reflection', {
     this.xrLightProbe = null;
     if (this.probeLight) {
       this.probeLight.components.light.light.intensity = 0;
+      this.needsVREnvironmentUpdate = true;
+      this.el.object3D.environment = this.cubeRenderTarget.texture;
     }
-    this.needsVREnvironmentUpdate = true;
-    this.el.object3D.environment = this.cubeRenderTarget.texture;
   },
   startLightProbe: function () {
     this.needsLightProbeUpdate = true;