Don't throw an exception if timer canceled while sleeping.
Don't throw an exception if timer canceled while sleeping.

It is a valid situation that may happen sometimes in threading,
so just quietly clean ourselves up and don't throw an
exception.

Signed-off-by: Chris Lalancette <281cd07d7578d97c83271fbbf2faddb83ab3791c@openrobotics.org>

ros2/rclpy,ros2/rclpy