Fix: autodisc: possible use-after-free

Reported-by: scan-build: Memory error Use-after-free
Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: Icfb8a6640a096369d51ba1c04ce43d043af7af59
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1971
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>