Follow up to r1330410, fix a segfault bug exposed by svnadmin test 28.
Follow up to r1330410, fix a segfault bug exposed by svnadmin test 28.

* subversion/libsvn_repos/hooks.c
  (run_hook_cmd): Do not attempt to close a file that wasn't opened.

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