Fix slice computation

typon/include/python/builtins/slice.hpp

@@ -42,10 +42,14 @@ struct PySlice {
 
     if (this->start == std::nullopt) {
       res.start = res.step < 0 ? PY_SSIZE_T_MAX : 0;
+    } else {
+      res.start = this->start.value();
     }
 
     if (this->stop == std::nullopt) {
       res.stop = res.step < 0 ? PY_SSIZE_T_MIN : PY_SSIZE_T_MAX;
+    } else {
+      res.stop = this->stop.value();
     }
 
     auto len = PySlice_AdjustIndices(seq_length, &res.start, &res.stop, res.step);