Fix: uninitialized directory handle finalized on error path

Fix: uninitialized directory handle finalized on error path

relay_create_trace_chunk() creates a session output directory handle
and assigns it to a trace chunk. Since a handle doesn't have a
dedicated "uninitialized" state, reduce its lifetime and don't
generically finalize it in error paths.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>