Follow-up to r1575628: Reinstantiate code that got removed accidentally.

* subversion/libsvn_fs_fs/index.c
  (l2p_page_info_copy): Actually read the page table entry.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1576801 13f79535-47bb-0310-9956-ffa450edef68