Avoid undefined behavior (and crashing) within FSFS and FSX when
there is no changes cache.

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__get_changes): Avoid possible uninitialized variable access by
    setting FOUND to FALSE in case we do not have a CHANGES_CACHE.
* subversion/libsvn_fs_x/cached_data.c
  (svn_fs_x__get_changes): Avoid possible uninitialized variable access by
    setting FOUND to FALSE in case we do not have CHANGES_CACHE and
    CHANGES_CONTAINER_CACHE.

Patch by: Evgeny Kotkov


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1549766 13f79535-47bb-0310-9956-ffa450edef68