Permit to call starpu_data_wont_use on data with no value, just make it do nothing

src/datawizard/user_interactions.c

@@ -686,6 +686,9 @@ static void _starpu_data_wont_use(void *data)
 
 void starpu_data_wont_use(starpu_data_handle_t handle)
 {
+	if (!handle->initialized)
+		/* No value atm actually */
+		return;
 	_STARPU_TRACE_DATA_WONT_USE(handle);
 	starpu_data_acquire_on_node_cb_sequential_consistency_quick(handle, STARPU_ACQUIRE_NO_NODE_LOCK_ALL, STARPU_R, _starpu_data_wont_use, handle, 1, 1);
 }