Fix: relayd: return from function without unlocking session lock

Fix: relayd: return from function without unlocking session lock

Some error paths in relay_close_trace_chunk() skip the unlock
of the relay_session's lock.

412203 Missing unlock

May result in deadlock if there is another attempt to acquire the
lock.

In relay_close_trace_chunk: Missing a release of a lock on a
path (CWE-667)

Reported-by: Coverity Scan
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I43187959abf00e761f7a255f4af7cd53e0c451fb