Follow-up to r1605195:  Fix SEGFAULT for log in authz mode.

* subversion/libsvn_repos/log.c
  (detect_changed): When filtering the hash, we must either remove
                    unwanted entries or add wanted ones to a new hash.
                    Otherwise, unwanted entries keep their old, internal
                    data type.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/authzperf@1615360 13f79535-47bb-0310-9956-ffa450edef68