Fix a bug that caused 'svnversion --version .' to crash.
Fix a bug that caused 'svnversion --version .' to crash.

* subversion/libsvn_subr/opt.c
  (svn_opt_print_help): don't bother trying to print subcommand help if we
   don't actually have a command table, as is the case in svnversion.

Reported By:  Manuel Arias <manuel.arias at gmail.com>

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