connection: Move object lookup out of wl_connection_demarshal()

On the client side where we queue up multiple events before dispatching, we
need to look up the receiving proxy and argument proxies immediately before
calling the handler.  Between queueing up multiple events and eventually
invoking the handler, previous handlers may have destroyed some of the
proxies.

src/wayland-private.h

@@ -99,6 +99,9 @@ wl_connection_demarshal(struct wl_connection *connection,
 			struct wl_map *objects,
 			const struct wl_message *message);
 
+int
+wl_closure_lookup_objects(struct wl_closure *closure, struct wl_map *objects);
+
 void
 wl_closure_invoke(struct wl_closure *closure,
 		  struct wl_object *target, void (*func)(void), void *data);