Fix: bt_stream_common_finalize(): check `stream->destroy_listeners`

Fix: bt_stream_common_finalize(): check `stream->destroy_listeners`

Issue
=====
In bt_stream_common_finalize(), `stream->destroy_listeners` is not
checked before calling iterating the array to call the destroy
listeners. This can happen if the stream is partially initialized and
then destroyed when there's an error in bt_stream_common_initialize().

Solution
========
Check `stream->destroy_listeners` before iterating the destroy listener
array.

Known drawbacks
===============
None.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>