Until now, the value returned by ovni_thread_isready() was still
non-zero when the thread stream was destroyed in ovni_thread_free()
This was making it impossible to detect when a stream was destroyed.
This change makes it return 0 after ovni_thread_free() by using a new
finished flag. The flag keeps track on then the stream is destroyed,
preventing double initialization of a free stream.
Rodrigo Arias
0439399f05