Resolve issue #4304, by detecting some kinds of shadowed nodes before trying to
set a file read only.

* subversion/libsvn_wc/adm_ops.c
  (svn_wc_remove_lock2): Handle invalid status err.

* subversion/tests/cmdline/lock_tests.py
  (lock_unlock_deleted): Remove XFail marker.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1438125 13f79535-47bb-0310-9956-ffa450edef68