McdDispatcher: don't allow startup locks to be released once dispose is called
McdDispatcher: don't allow startup locks to be released once dispose is called

If we haven't started to dispatch channels, and now we're
self-destructing, we certainly don't want to start dispatching channels
to whatever's left of our handlers (in practice, the channels would
probably be closed as undispatchable).

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control