layout name can be null

[krumelmonster]

If a layout is not in builtin_channel_layouts, the corresponding char* SoundIoDevice::name will be NULL which should either be documented here: https://github.com/andrewrk/libsoundio/blob/8ab36069123a8b38e247ace55f8a6b3e6ee14f5f/soundio/soundio.h#L307 or changed to a generic name like "unknown layout" here: https://github.com/andrewrk/libsoundio/blob/8ab36069123a8b38e247ace55f8a6b3e6ee14f5f/src/channel_layout.c#L435