linux-alsa: stop reopen thread before destroying abort_event

This was found by inspecting a crash backtrace that aborted in
glibc's __pthread_mutex_cond_lock from os_event_timedwait in the ALSA
plugin's reopen thread.

alsa_destroy was destroying abort_event without first stopping and
joining the thread, which also waits on that event. If destruction
wins the race, the waiter can wake and try to relock a mutex belonging
to an event that has already been destroyed. Stop the reopen thread
first so abort_event stays valid for the lifetime of the
wait.

Author: Charles

plugins/linux-alsa/alsa-input.c

@@ -154,6 +154,8 @@ void alsa_destroy(void *vptr)
 {
 	struct alsa_data *data = vptr;
 
+	_alsa_stop_reopen(data);
+
 	if (data->handle)
 		_alsa_close(data);