batched-bench : fix oob write

ggml-ci

tools/batched-bench/batched-bench.cpp

@@ -130,7 +130,10 @@ int main(int argc, char ** argv) {
                         common_batch_add(batch, 0, i, { j }, false);
                     }
                 }
-                batch.logits[batch.n_tokens - 1] = true;
+
+                if (batch.n_tokens > 0) {
+                    batch.logits[batch.n_tokens - 1] = true;
+                }
 
                 const auto t_pp_start = ggml_time_us();