Resource leak when `subprocess_create_ex()` fails

The `subprocess_create_ex()` function just has `return -1` in case of an error, without properly closing already open file descriptors. Example: https://github.com/sheredom/subprocess.h/blob/7e59b6924aa0e1a595be86fdeb1d4c28835aa0b9/subprocess.h#L876-L880 In my test, trying to call this function with a non-existing command results in 6 more new FDs each time.