Don't crash when command-line client is run with no options.

* subversion/svn/help-cmd.c
  (svn_cl__help): Check opt_state before dereferencing it, since we
    can be called without a baton, and thus can end up with no
    opt_state.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/automatic-pager@1565000 13f79535-47bb-0310-9956-ffa450edef68