Ensure that failures to construct a window key will result in defined cache access behavior. We use the latest cache API improvements to skip cache access in that case.
Ensure that failures to construct a window key will result
in defined cache access behavior. We use the latest cache
API improvements to skip cache access in that case.

* subversion/libsvn_fs_fs/fs_fs.c
  (get_window_key): return NULL instead of "" upon failure

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion