2948 do not generate 0 as random 64-bit guid

*** 801,812 ****
--- 801,814 ----
          dsphys = dbuf->db_data;
          bzero(dsphys, sizeof (dsl_dataset_phys_t));
          dsphys->ds_dir_obj = dd->dd_object;
          dsphys->ds_flags = flags;
          dsphys->ds_fsid_guid = unique_create();
+         do {
                  (void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
                      sizeof (dsphys->ds_guid));
+         } while (dsphys->ds_guid == 0);
          dsphys->ds_snapnames_zapobj =
              zap_create_norm(mos, U8_TEXTPREP_TOUPPER, DMU_OT_DSL_DS_SNAP_MAP,
              DMU_OT_NONE, 0, tx);
          dsphys->ds_creation_time = gethrestime_sec();
          dsphys->ds_creation_txg = tx->tx_txg == TXG_INITIAL ? 1 : tx->tx_txg;
*** 2082,2093 ****
--- 2084,2097 ----
          dmu_buf_will_dirty(dbuf, tx);
          dsphys = dbuf->db_data;
          bzero(dsphys, sizeof (dsl_dataset_phys_t));
          dsphys->ds_dir_obj = ds->ds_dir->dd_object;
          dsphys->ds_fsid_guid = unique_create();
+         do {
                  (void) random_get_pseudo_bytes((void*)&dsphys->ds_guid,
                      sizeof (dsphys->ds_guid));
+         } while (dsphys->ds_guid == 0);
          dsphys->ds_prev_snap_obj = ds->ds_phys->ds_prev_snap_obj;
          dsphys->ds_prev_snap_txg = ds->ds_phys->ds_prev_snap_txg;
          dsphys->ds_next_snap_obj = ds->ds_object;
          dsphys->ds_num_children = 1;
          dsphys->ds_creation_time = gethrestime_sec();