Make the MS runtime checks happy that reported an access to an uninitialized
value (that would not actually be used later on).

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__get_changes): Always initialize changes_offset.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1547096 13f79535-47bb-0310-9956-ffa450edef68