Crash caused by concurrent access to the sndio MIDI handle

On 2026-05-25, the OpenBSD LMMS port received a patch ([`include/MidiSndio.h`](https://cvsweb.openbsd.org/checkout/ports/audio/lmms/patches/patch-include_MidiSndio_h,v?rev=1.1), [`src/core/midi/MidiSndio.cpp`](https://cvsweb.openbsd.org/checkout/ports/audio/lmms/patches/patch-src_core_midi_MidiSndio_cpp,v?rev=1.1)) with the following message:

```
ratchov

Add the necessary locking to the sndio MIDI backend

Fixes crashes caused concurrent accesses to the sndio MIDI handle.

ok rsadowski
```

I haven't personally replicated this crash but it seems likely to be a problem.

The simplest solution would be to apply these patches upstream (here) but they use a mutex to solve the problem which is not ideal.