Fixed private member access in init_branches()

exprtk.hpp

@@ -12759,7 +12759,11 @@ namespace exprtk
                      return false;
 
                   ts.size = 1;
+#ifdef exprtk_enable_vector_runtime_checks
                   ts.data = var->value_ptr();
+#else
+                  ts.data = &var->ref();
+#endif
                   ts.type = type_store_t::e_scalar;
                }
                else