Add missing StepCounter call in IGIA

The `counter` keeps track of how many Pareto points we find, and how many "steps" were required to climb up to the Pareto front.

In the IGIA, we don't count the very first starting point (when we throw the dart). This change adds it back in.

(See [here](https://github.com/TeamAmalgam/kodkod/blob/d71ee0869681059a08789a1132b8d3c900b75c55/src/kodkod/multiobjective/algorithms/GuidedImprovementAlgorithm.java#L59) for the corresponding `countStep()` in GIA.)