Fix an error leak in the hook script invocation code.
Fix an error leak in the hook script invocation code.

* subversion/libsvn_repos/hooks.c
  (run_hook_cmd): If check_hook_result() returns an error, do not leak this
    error and do not attempt to read output from a hook that wasn't started.

Reported by: Walter Klust <wklust@elego.de>

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