BUG/MAJOR: peers: initialize s->buffer_wait when creating the session

Commit bf883e0 ("MAJOR: session: implement a wait-queue for sessions who
need a buffer") introduced in 1.6 forgot to initialize the buffer_wait
list when the session is initiated by an applet for a peer, resulting in
a crash. Thanks to Chris Kopp for reporting the issue.

src/peers.c

@@ -1134,6 +1134,7 @@ static struct session *peer_session_create(struct peer *peer, struct peer_sessio
 
 	LIST_ADDQ(&sessions, &s->list);
 	LIST_INIT(&s->back_refs);
+	LIST_INIT(&s->buffer_wait);
 
 	s->flags = SN_ASSIGNED|SN_ADDR_SET;