Make sure node is known before getting its kind

tests/datawizard/specific_node.c

@@ -36,6 +36,7 @@ void specific_kernel(void *descr[], void *arg)
 {
 	(void)arg;
 	int node = starpu_task_get_current_data_node(0);
+	STARPU_ASSERT(node >= 0);
 	STARPU_ASSERT(starpu_node_get_kind(node) == STARPU_CPU_RAM);
 	unsigned *dataptr = (unsigned*) STARPU_VARIABLE_GET_PTR(descr[0]);