On the verify-keep-going branch, a follow-up to r1546059.

* subversion/libsvn_repos/dump.c
  (notify_verification_error): Restore notify_func == NULL check. It is
   needed in this function.
  (notify_verification_error_summary): And remove it here, which is what
   I intended to do in r1546059.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/verify-keep-going@1546063 13f79535-47bb-0310-9956-ffa450edef68