Fix for possible freeze in Recorder::stop() (#1381)

* Fix for possible freeze in Recorder::stop()

- It was possible a freeze in recorder due to the race condition when
calling Recorder::stop() while event publisher thread hasn't been fully
started yet.

Signed-off-by: Michael Orlov <[email protected]>

* Move event_publisher_thread_wake_cv_.notify_all() out of the mutex lock

Signed-off-by: Michael Orlov <[email protected]>

---------

Signed-off-by: Michael Orlov <[email protected]>
(cherry picked from commit c6cc69a)

# Conflicts:
#	rosbag2_transport/src/rosbag2_transport/recorder.cpp