Calling SDL_Init() in different threads in the same process crashes.
In this SDL2 code X11_XOpenDisplay() will be a null pointer on the second thread;
if (SDL_X11_LoadSymbols()) {
display = X11_XOpenDisplay(NULL);
This becomes a problem when monado starts the debug UI in a thread,
and then an OpenXR client application tries to initialize SDL.
Two consecutive SDL_Init() in the same thread is harmless though.