lib: append error in simple_sink_consume only if error status

If the consume_func returns _AGAIN, we will append an error cause.  That
is wrong because _AGAIN is not an error cause.  Check for negative
status values instead of just != OK.

Change-Id: Ibc03a1e9eb25de5ec39af5148c8e235498c57b64
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2358
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>

src/lib/graph/component-class-sink-simple.c

@@ -178,7 +178,7 @@ enum bt_component_class_sink_consume_method_status simple_sink_consume(
 	/* Call user's "consume" function */
 	status = data->init_method_data.consume_func(data->msg_iter,
 		data->init_method_data.user_data);
-	if (status != BT_FUNC_STATUS_OK) {
+	if (status < 0) {
 		BT_LIB_LOGW_APPEND_CAUSE(
 			"Simple sink component's user's \"consume\" function failed: "
 			"status=%s, %![comp-]+c",