Follow-up to r1469520: Remove another initialization that's not needed.

* subversion/libsvn_fs_fs/tree.c (open_path): Reorder code to avoid
   premature initialization.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1481870 13f79535-47bb-0310-9956-ffa450edef68