Minor restructure for platformio compatibility

src/evaluate.c

@@ -68,6 +68,7 @@ struct ucl_object *ucl_evaluate_list(struct ucl* state, struct ucl_scope *scope,
         return ucl_evaluate_builtin_form(state, scope, list);
     } else {
         assert(0);
+        UCL_COND_OR_RET_ERROR(false, "Unreachable error in ucl_evaluate_list");
     }
 }