If during WATCHLIST_NOTIFY{,_MATCHES,_NO_ARGS} one of the watch
notify callback triggers a call to watchlist_destroy, give up calling
remaining watches and destroy the watchlist without crashing. This is
useful in frame-xchg.c (P2P use case) where a frame watch may trigger
a move to a new state after receiving a specific frame, and remove one
group of frame watches (including its watchlist) to create a different
group.
Andrew Zaborowski