Update webXRSessionManager.ts
Update webXRSessionManager.ts

Avoid overriding a value that was passed in options.
BabylonJS/Babylon.js,sebavan/Babylon.js,RaananW/Babylon.js,RaananW/Babylon.js,BabylonJS/Babylon.js,sebavan/Babylon.js,BabylonJS/Babylon.js,RaananW/Babylon.js,sebavan/Babylon.js