player/client: reduce log level for hooks not sent to clients

If a hook event can't be sent to a client because it no longer exists,
stop logging it as a warning, as there is no way for a client to remove
hooks, so it is expected that the hook can't be sent. This is documented
in libmpv/client.h.

If the hook event can't be sent because the event queue is full, keep
logging as warning.

player/command.c

@@ -216,7 +216,8 @@ static int invoke_hook_handler(struct MPContext *mpctx, struct hook_handler *h)
     char *name = mp_tprintf(22, "@%"PRIi64, h->client_id);
     int r = mp_client_send_event(mpctx, name, reply_id, MPV_EVENT_HOOK, m);
     if (r < 0) {
-        MP_WARN(mpctx, "Sending hook command failed. Removing hook.\n");
+        MP_MSG(mpctx, mp_client_id_exists(mpctx, h->client_id) ? MSGL_WARN : MSGL_V,
+               "Sending hook command failed. Removing hook.\n");
         hook_remove(mpctx, h);
         mp_wakeup_core(mpctx); // repeat next iteration to finish
     }