bit safer way of overriding.

Don't want to add null overrides for things that were not there already

dist-header.js

@@ -1,22 +1,25 @@
-XRDisplay = null
+/* if there is a navigator.xr, clear it out */
-XRSession = null
+if(typeof navigator.xr != 'undefined') {
-XRSessionCreateParameters = null
+    if(typeof XRDisplay != 'undefined') { XRDisplay = null }
-Reality = null
+    if(typeof XRSession != 'undefined') { XRSession = null }
-XRPointCloud = null;
+    if(typeof XRSessionCreateParameters != 'undefined') { XRSessionCreateParameters = null }
-XRLightEstimate = null;
+    if(typeof Reality != 'undefined') { Reality = null }
-XRAnchor = null;
+    if(typeof XRPointCloud != 'undefined') { XRPointCloud = null }
-XRPlaneAnchor = null;
+    if(typeof XRLightEstimate != 'undefined') { XRLightEstimate = null }
-XRFaceAnchor = null;
+    if(typeof XRAnchor != 'undefined') { XRAnchor = null }
-XRImageAnchor = null;
+    if(typeof XRPlaneAnchor != 'undefined') { XRPlaneAnchor = null }
-XRAnchorOffset = null;
+    if(typeof XRFaceAnchor != 'undefined') { XRFaceAnchor = null }
-XRStageBounds = null;
+    if(typeof XRImageAnchor != 'undefined') { XRImageAnchor = null }
-XRStageBoundsPoint = null;
+    if(typeof XRAnchorOffset != 'undefined') { XRAnchorOffset = null }
-XRPresentationFrame = null;
+    if(typeof XRStageBounds != 'undefined') { XRStageBounds = null }
-XRView = null;
+    if(typeof XRStageBoundsPoint != 'undefined') { XRStageBoundsPoint = null }
-XRViewport = null;
+    if(typeof XRPresentationFrame != 'undefined') { XRPresentationFrame = null }
-XRCoordinateSystem = null;
+    if(typeof XRView != 'undefined') { XRView = null }
-XRViewPose = null;
+    if(typeof XRViewport != 'undefined') { XRViewport = null }
-XRLayer = null;
+    if(typeof XRCoordinateSystem != 'undefined') { XRCoordinateSystem = null }
-XRWebGLLayer = null 
+    if(typeof XRViewPose != 'undefined') { XRViewPose = null }
-XRVideoFrame = null;
+    if(typeof XRLayer != 'undefined') { XRLayer = null }
-
+    if(typeof XRWebGLLayer != 'undefined') { XRWebGLLayer = null }
+    if(typeof XRVideoFrame != 'undefined') { XRVideoFrame = null }
+    //navigator.xr = null;
+}