tork(1): fix crash when typing in `t` without args

lib/tork/cliapp.rb:65:in `test': wrong number of arguments (0 for 2..3) (ArgumentError)
        from lib/tork/cliapp.rb:65:in `recv'
        from lib/tork/server.rb:46:in `block (2 levels) in loop'
        from lib/tork/server.rb:38:in `each'
        from lib/tork/server.rb:38:in `block in loop'
        from lib/tork/server.rb:36:in `catch'
        from lib/tork/server.rb:36:in `loop'
        from lib/tork/cliapp.rb:9:in `loop'
        from bin/tork:128:in `<top (required)>'