Silence a compiler "potentially uninitialized" compiler warning that is
actually a false positive but the dependencies are obviously too complex
for GCC to understand.

* subversion/libsvn_fs_fs/tree.c
  (open_path): Initialize REST to NULL.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1590440 13f79535-47bb-0310-9956-ffa450edef68