Fix: stream.c: autopopulate timestamp fields even when not mapped to CC

To remain backward compatible with Babeltrace 1's CTF writer,
automatically set the event header `timestamp` fields (when appending
the event) and packet context `timestamp_begin` and `timestamp_end`
fields (on stream flush) when the stream's class has a registered CTF
writer clock, even if the field's types are not mapped to a clock class.

If the field is mapped to a clock class, then it is automatically set
when this mapped clock class is the same as the stream's class's clock's
class.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

lib/ctf-ir/stream.c

@@ -495,16 +495,7 @@ int set_packet_context_timestamp_field(struct bt_stream *stream,
 
 	field_mapped_clock_class =
 		bt_field_type_integer_get_mapped_clock_class(field->type);
-	if (!field_mapped_clock_class) {
-		BT_LOGV("Packet context's `%s` field's type is not mapped to a clock class: skipping: "
-			"stream-addr=%p, stream-name=\"%s\", "
-			"field-addr=%p, ft-addr=%p", field_name,
-			stream, bt_stream_get_name(stream),
-			field, field->type);
-		goto end;
-	}
-
-	if (field_mapped_clock_class !=
+	if (field_mapped_clock_class && field_mapped_clock_class !=
 			stream->stream_class->clock->clock_class) {
 		BT_LOGV("Packet context's `%s` field's type is not mapped to the stream's clock's class: skipping: "
 			"stream-addr=%p, stream-name=\"%s\", "
@@ -1212,7 +1203,8 @@ static int auto_populate_event_header(struct bt_stream *stream,
 		mapped_clock_class =
 			bt_field_type_integer_get_mapped_clock_class(
 				timestamp_field->type);
-		if (mapped_clock_class == stream_class_clock_class) {
+		if (!mapped_clock_class ||
+				mapped_clock_class == stream_class_clock_class) {
 			uint64_t timestamp;
 
 			ret = bt_ctf_clock_get_value(