Segfault in ReferenceObj_Read when a reference's row can't be read before any other #282

/*
 * Reproduction: ReferenceObj_Read on a reference whose rows can't be read.
 *
 * Opens an aligned (cSRA) archive whose external references are not available (e.g. a copy
 * of the .sra alone, with remote access disabled), and reads the first bases of reference
 * <index> before any other. TableReader_ReadRow fails, but ReferenceObj_Read then reads the
 * row's SEQ_LEN cell anyway; no row has been read yet, so the cell's pointer is NULL.
 *
 * Usage: missing-reference-read <archive.sra> <index>
 */
#include <align/reference.h>
#include <klib/rc.h>
#include <vdb/database.h>
#include <vdb/manager.h>

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

int main(int argc, char *argv[])
{
    const VDBManager *mgr = NULL;
    const VDatabase *db = NULL;
    const ReferenceList *list = NULL;
    const ReferenceObj *obj = NULL;
    uint8_t bases[5000];
    INSDC_coord_len written = 0;
    rc_t rc;

    if (argc != 3) {
        fprintf(stderr, "usage: %s <archive.sra> <index>\n", argv[0]);
        return 2;
    }
    rc = VDBManagerMakeRead(&mgr, NULL);
    if (rc == 0)
        rc = VDBManagerOpenDBRead(mgr, &db, NULL, "%s", argv[1]);
    if (rc == 0)
        rc = ReferenceList_MakeDatabase(&list, db, ereferencelist_4na, 0, NULL, 0);
    if (rc == 0)
        rc = ReferenceList_Get(list, &obj, (uint32_t)atoi(argv[2]));
    if (rc != 0) {
        fprintf(stderr, "setup failed: rc=%u\n", rc);
        return 2;
    }
    rc = ReferenceObj_Read(obj, 0, sizeof(bases), bases, &written);
    {
        const char *seq_id = NULL;
        ReferenceObj_SeqId(obj, &seq_id);
        printf("%s: ReferenceObj_Read rc=%u written=%u\n", seq_id, rc, written);
    }
    ReferenceObj_Release(obj);
    ReferenceList_Release(list);
    VDatabaseRelease(db);
    VDBManagerRelease(mgr);
    return rc == 0 ? 0 : 1;
}