Make zero step numerical for loop use the positive number evaluation

src/Evaluator/Evaluator.cpp

@@ -129,7 +129,7 @@ namespace Porygon::Evaluation {
         auto identifier = statement -> GetIdentifier();
         this -> _evaluationScope -> CreateVariable(identifier, nullptr);
         auto block = (BoundBlockStatement*)statement -> GetBlock();
-        if (step > 0){
+        if (step >= 0){
             for (long i = start; i <= end; i += step){
                 this -> _evaluationScope -> SetVariable(identifier, make_shared<IntegerEvalValue>(i));
                 for (auto s: *block->GetStatements()) {