Fix issue with the computation (orders of the call to rand_get)

bench/bench-mlib.c

@@ -116,7 +116,8 @@ test_dict(unsigned long  n)
 #endif
   M_LET(dict, DICT_OPLIST(ulong)) {
     for (size_t i = 0; i < n; i++) {
-      dict_ulong_set_at(dict, rand_get(), rand_get() );
+      unsigned long key = rand_get();
+      dict_ulong_set_at(dict, key, rand_get() );
     }
     rand_init();
     unsigned int s = 0;