git_shorten_add segfaults when adding to many objects.

backtrace.txt

#0  0x00007ffff7b55d18 in push_leaf (os=0x6011f0, idx=32767, push_at=10, 
    oid=0x7fffffffdebb "fb1970fb98c05d1fc75a21cc9b977") at /home/mero/src/libgit2/src/oid.c:279
        node = 0x7ffff6588ff0
        leaf = 0x7ffff6389010
        idx_leaf = -32768
#1  0x00007ffff7b55edc in git_oid_shorten_add (os=0x6011f0, 
    text_oid=0x7fffffffdeb0 "d8f11d9ac1afb1970fb98c05d1fc75a21cc9b977")
    at /home/mero/src/libgit2/src/oid.c:388
        tail = 0x7fffffffdeba "afb1970fb98c05d1fc75a21cc9b977"
        c = 10
        node = 0x7ffff7f06ff0
        i = 10
        is_leaf = true
        idx = 32767
#2  0x00000000004009ae in odb_foreach_cb (id=0x7ffff7fde078, payload=0x6011f0) at test.c:13
        s = 0x6011f0
        sid = "d8f11d9ac1afb1970fb98c05d1fc75a21cc9b977"
#3  0x00007ffff7b43daa in git_pack_foreach_entry (p=0x60b2a0, cb=0x40096c <odb_foreach_cb>, 
    data=0x6011f0) at /home/mero/src/libgit2/src/pack.c:1041
        index = 0x7ffff7fdc408 ""
        current = 0x7ffff7fdf2f8 ""
        i = 253
        __PRETTY_FUNCTION__ = "git_pack_foreach_entry"
#4  0x00007ffff7b34fa5 in pack_backend__foreach (_backend=0x601670, cb=0x40096c <odb_foreach_cb>, 
    data=0x6011f0) at /home/mero/src/libgit2/src/odb_pack.c:443
        error = 0
        p = 0x60b2a0
        backend = 0x601670
        i = 7
        __PRETTY_FUNCTION__ = "pack_backend__foreach"
#5  0x00007ffff7b753cc in git_odb_foreach (db=0x602900, cb=0x40096c <odb_foreach_cb>, 
    payload=0x6011f0) at /home/mero/src/libgit2/src/odb.c:819
        b = 0x601670
        error = 0
        i = 1
        internal = 0x601720
#6  0x0000000000400aee in main (argc=2, argv=0x7fffffffe168) at test.c:44
        repo = 0x6010b0
        db = 0x602900
        s = 0x6011f0

gistfile1.c

#include <git2.h>
#include <stdio.h>
#include <stdlib.h>

int odb_foreach_cb(const git_oid *id, void *payload) {
    git_oid_shorten *s = (git_oid_shorten *)payload;
    char sid[41];
    sid[40] = '\0';
    git_oid_fmt(sid, id);

    if (git_oid_shorten_add(s, sid) < 0) {
        fprintf(stderr, "shorten_add\n");
        return -1;
    }
    return 0;
}

int main(int argc, char **argv) {
    if (argc < 2) {
        fprintf(stderr, "Usage: %s path\n", argv[0]);
        return 1;
    }

    git_repository *repo;
    if (git_repository_open(&repo, argv[1])) {
        fprintf(stderr, "Could not open repo\n");
        return 1;
    }

    git_odb *db;
    if (git_repository_odb(&db, repo)) {
        fprintf(stderr, "Could not open odb\n");
        return 1;
    }

    git_oid_shorten *s = git_oid_shorten_new(4);
    if (s == NULL) {
        fprintf(stderr, "OOM\n");
        return 1;
    }

    if (git_odb_foreach(db, &odb_foreach_cb, (void *)s)) {
        fprintf(stderr, "foreach\n");
        return 1;
    }
    return 0;
}