We explicitely wait for the last task, so it must not be detached

tests/core/empty_task_chain.c

@@ -37,6 +37,9 @@ int main(int argc, char **argv)
 			ret = starpu_task_submit(tasks[i]);
 			STARPU_ASSERT(!ret);
 		}
+
+		if (i == (N-1))
+			tasks[i]->detach = 0;
 	}
 
 	ret = starpu_task_submit(tasks[0]);