On VR session start with positional tracking disabled, the pose would
have an offset applied but it was supposed to start exactly at the
landmark position.
Issue is that we applied the offset to cancel out the position offset
reported by the OpenXR runtime incorrectly. We only want to do that if
positional tracking is enabled, because if not we don't even apply the
runtime's position offset. So we'd cancel something out that wasn't
there.
ab3a651515