With OpenXR built, every RETRO_DEVICE_POINTER and LIGHTGUN read walked
the core port's users to gather their slots before asking the headset,
which answers false at once whenever its laser does not drive a core's
pointer - nearly always without a headset. The headset is now asked
first whether it does, and the walk is skipped when not.
openxr_input_test checks the answer with the laser off and on.