Handle event loop watcher failure modes

When alibuEv event watcher callback has `UEV_ERROR` in the events mask
we must handle the error.  Unfortunately, in most cases there is not
much we can do but ignore it or log the error.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

src/service.c

@@ -82,6 +82,7 @@ static void service_timeout_cb(uev_t *w, void *arg, int events)
 {
 	svc_t *svc = arg;
 
+	/* Ignore any UEV_ERROR, we're a one-shot cb so just run it. */
 	svc->timer_cb(svc);
 }