flst_add_to_empty(): read len only in debug build

Author: kevgs

storage/innobase/fut/fut0lst.cc

@@ -40,7 +40,7 @@ flst_add_to_empty(
 {
 ulint	space;
 fil_addr_tnode_addr;
-ulint	len;
+ulint	len = 0;
 
 ut_ad(mtr && base && node);
 ut_ad(base != node);
@@ -50,7 +50,7 @@ flst_add_to_empty(
 ut_ad(mtr_memo_contains_page_flagged(mtr, node,
  MTR_MEMO_PAGE_X_FIX
  | MTR_MEMO_PAGE_SX_FIX));
-len = flst_get_len(base);
+ut_d(len = flst_get_len(base));
 ut_a(len == 0);
 
 buf_ptr_get_fsp_addr(node, &space, &node_addr);