getopt: fix null pointer arithmetic ub

[musl] / src / string / wmemcpy.c

#include <wchar.h>

wchar_t *wmemcpy(wchar_t *restrict d, const wchar_t *restrict s, size_t n)
{
        wchar_t *a = d;
        while (n--) *d++ = *s++;
        return a;
}