Model with non-named argument

[pedro-andrade-inpe]

Fix the bug when one creates a model with a non-named argument, as in the example below:

Tub = Model{
     water = 40,
     period = 0,01,
     finalTime = 20,
     init = function(model)
            model.chart = Chart{
                target = model,
                select = "water"
            }

            model.timer = Timer{
                Event{action = model.chart},
          }
     end
}