add trivial getter method for q_lvl to be consistent with other ones

include/evalhyd/detail/probabilist/evaluator.hpp

@@ -158,6 +158,11 @@ namespace evalhyd
                 }
             }
 
+            auto get_q_lvl()
+            {
+                return _q_lvl;
+            }
+
             bool is_high_flow_event()
             {
                 if (_events.has_value())
@@ -337,7 +342,7 @@ namespace evalhyd
                 if (!itv_bnds.has_value())
                 {
                     itv_bnds = elements::calc_itv_bnds(
-                            q_prd, get_c_lvl(), _q_lvl,
+                            q_prd, get_c_lvl(), get_q_lvl(),
                             n_sit, n_ldt, n_itv, n_tim
                     );
                 }
@@ -394,7 +399,7 @@ namespace evalhyd
                 if (!qs.has_value())
                 {
                     qs = intermediate::calc_qs(
-                            q_obs, get_q_qnt(), n_mbr, _q_lvl
+                            q_obs, get_q_qnt(), n_mbr, get_q_lvl()
                     );
                 }
                 return qs.value();