In the vr samples, handle rejection of getVRDisplays for the case when the API...

In the vr samples, handle rejection of getVRDisplays for the case when the API is available but WebVR is not supported

examples/js/vr/WebVR.js

@@ -191,7 +191,7 @@ var WEBVR = {
 
 					}
 
-				} );
+				} ).catch( showVRNotFound );
 
 			return button;