rgw: fix osd crashes when execute "radosgw-admin bi list --max-entrie…

…s=1" command

Fixes: http://tracker.ceph.com/issues/17745
Signed-off-by: weiqiaomiao <wei.qiaomiao@zte.com.cn>
(cherry picked from commit 51a4405)

src/cls/rgw/cls_rgw.cc

@@ -2375,9 +2375,9 @@ static int rgw_bi_list_op(cls_method_context_t hctx, bufferlist *in, bufferlist
 
   string filter = op.name;
 #define MAX_BI_LIST_ENTRIES 1000
-  int32_t max = (op.max < MAX_BI_LIST_ENTRIES ? op.max : MAX_BI_LIST_ENTRIES);
+  int32_t max = (op.max < MAX_BI_LIST_ENTRIES ? op.max : MAX_BI_LIST_ENTRIES) + 1; /* one extra entry for identifying truncation */
   string start_key = op.marker;
-  int ret = list_plain_entries(hctx, op.name, op.marker, max, &op_ret.entries) + 1; /* one extra entry for identifying truncation */
+  int ret = list_plain_entries(hctx, op.name, op.marker, max, &op_ret.entries); 
   if (ret < 0) {
     CLS_LOG(0, "ERROR: %s(): list_plain_entries retured ret=%d", __func__, ret);
     return ret;