The keys and values of device_hash are pairs
`(SDL_AudioDeviceID devid, void *dev)` where dev can be either a
`SDL_AudioDevice *` or a `SDL_LogicalAudioDevice *`, depending on
bit 1 of devid.
We can confirm that we have got this right by looking at the
instance_id member, because logical audio devices happen to start with
the devid, whereas physical devices start with a pointer which is
unlikely to match the devid by chance.
Signed-off-by: Simon McVittie <smcv@collabora.com>
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