SDL_Process stdin errors with SDL_FlushIO

[Semphriss]

I'm opening this issue because I'm not sure if there's a particular reason to work that way, but I noticed I can't flush a process input pipe.

#include <SDL3/SDL.h>

int main(void)
{
  const char *args[] = { "cat", NULL };
  char buf[16] = { '\0' };

  SDL_Init(0);

  SDL_Process *proc = SDL_CreateProcess(args, true);
  SDL_IOStream *in = SDL_GetProcessInput(proc);
  SDL_IOStream *out = SDL_GetProcessOutput(proc);

  SDL_WriteIO(in, "ab", 2);
  bool success = SDL_FlushIO(in);  // <-- Here
  SDL_Log("Success: %d\n", success);
  SDL_Log("%s\n", SDL_GetError());

  SDL_Delay(10); // Give the child process some time to pass its stdin to stdout

  SDL_ReadIO(out, buf, sizeof(buf));
  SDL_Log("'%s'\n", buf);

  SDL_KillProcess(proc, false);
  SDL_WaitProcess(proc, true, NULL);
  SDL_DestroyProcess(proc);

  SDL_Quit();
  return 0;
}

Output:

Success: 0
Error flushing datastream: Invalid argument
'ab'

Writing to the child process' input seems to automatically flush, so the call to SDL_FlushIO doesn't seem to be necessary. However, would it be better to make that function a successful no-op instead?