Fix svn_repos_fs_change_rev_prop4() not loading the hook environment when only
the pre_revprop_change_hook was requested.

* subversion/libsvn_repos/fs-wrap.c
  (svn_repos_fs_change_rev_prop4): Change one of the duplicated
    use_post_revprop_change_hook variables in the expression to
    use_pre_revprop_change_hook.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1469556 13f79535-47bb-0310-9956-ffa450edef68