Fix other cause of intermittent timing-dependent crash at shutdown...

... AudioIO holds a weak pointer to its listener so there is no dangling
pointer

src/ProjectAudioManager.h

@@ -20,6 +20,7 @@ struct AudioIOStartStreamOptions;
 class ProjectAudioManager final
    : public ClientData::Base
    , public AudioIOListener
+   , public std::enable_shared_from_this< ProjectAudioManager >
 {
 public:
    static ProjectAudioManager &Get( AudacityProject &project );