On the fsx-id branch:  Get rid of another NODEREV->ID access.

* subversion/libsvn_fs_x/low_level.c
  (read_rep_offsets): The error message shall display the noderev ID instead
                      of the full ID.  Also, the noderev ID cannot be NULL.
  (svn_fs_x__read_noderev): Update caller.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsx-id@1645985 13f79535-47bb-0310-9956-ffa450edef68