Avoid JSON errors on Windows with no sound devices

[alef]

Summary

Bugfixes "Avoid JSON errors on Windows with no sound devices"

Purpose of change

One can forget to turn their Bluetooth device and be left without audio devices available.
In that case, the TILES+SOUND built game for Windows reports JSON errors loading soundset.

Describe the solution

Export sound_init_success from sdlsound.cpp and make init_interface() skip loading sound set at all when it is false.

Describe alternatives you've considered

Not sure why WinCreate() should initialize audio too.

Testing

Compiled, run, load, walk around. No errors (and no audio).
Connect the Bluetooth audio back: same but with audio.

Additional context