Minor consistency fix - even though the result returned by the previous
code was technically correct.

* subversion/libsvn_fs_util/fs-util.c
  (svn_fs__path_change_create_internal): Unused copyfrom revs should be
                                         initialized to -1 even if we
                                         correctly default to "copyfrom
                                         is unknown".


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1636733 13f79535-47bb-0310-9956-ffa450edef68