vhost: listen: protect listen port transfer between

...vhosts from vh destroy on zero refcount

https://github.com/warmcat/libwebsockets/issues/2343

lib/core-net/vhost.c

@@ -1272,8 +1272,23 @@ lws_vhost_destroy1(struct lws_vhost *vh)
 
 				if (v->lserv_wsi) {
 					/* req cx + vh lock */
+					/*
+					 * If the vhost sees it's being destroyed and
+					 * in the unbind the number of wsis bound to
+					 * it falls to zero, it will destroy the
+					 * vhost opportunistically before we can
+					 * complete the transfer.  Add a fake wsi
+					 * bind temporarily to disallow this...
+					 */
+					v->count_bound_wsi++;
 					__lws_vhost_unbind_wsi(vh->lserv_wsi);
 					lws_vhost_bind_wsi(v, v->lserv_wsi);
+
+					/*
+					 * ... remove the fake wsi bind
+					 */
+					v->count_bound_wsi--;
+
 					vh->lserv_wsi = NULL;
 				}