Don't parse expression on different line from return keyword

src/Evaluator/Evaluator.cpp

@@ -95,6 +95,7 @@ namespace Porygon::Evaluation {
         auto expression = statement->GetExpression();
         if (expression == nullptr) {
             this->_hasReturned = true;
+            this -> _returnValue = nullptr;
             return;
         }
         auto value = this->EvaluateExpression(expression);