Undefined behavior in bf_set_si

[cryptocode]

When passing INT64_MIN to bf_set_si I experience a sigtrap on my system. I believe this is due to undefined behavior on this line:

quickjs/libbf.c

Line 274 in 6e2e68f

ret = bf_set_ui(r, -a);

as this will attempt to negate INT64_MIN

Might need a special case, possibly something like this:

int bf_set_si(bf_t *r, int64_t a)
{
    int ret;

    // Special case as -INT64_MIN is undefined
    if (a == INT64_MIN) {
        ret = bf_set_ui(r, (uint64_t)INT64_MAX + 1); 
        r->sign = 1;
    } else if (a < 0) {
        ret = bf_set_ui(r, -a);
        r->sign = 1;
    } else {
        ret = bf_set_ui(r, a);
    }
    return ret;
}

[Emill]

Changing to bf_set_ui(r, -(uint64_t)a) would be simpler.