On the log-addressing branch:  follow-up to r1537174.

* subversion/libsvn_fs_fs/structure-indexes
  (Log-to-phys index.Index file format): fix another off-by-one mismatch; fix notation

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/log-addressing@1537176 13f79535-47bb-0310-9956-ffa450edef68