small notification fixes

nested/src/core/port.rs

@@ -50,6 +50,7 @@ where V::Msg: Clone {
     }
 
     pub fn add_observer(&self, observer: Arc<RwLock<dyn Observer<V>>>) {
+        self.update();
         self.cast.write().unwrap().add_observer(Arc::downgrade(&observer));
         observer.write().unwrap().reset(self.view.read().unwrap().clone());
     }

nested/src/vec/vec2seq.rs

@@ -43,15 +43,15 @@ where T: Clone + Send + Sync + 'static {
     fn reset(&mut self, view: Option<Arc<RwLock<Vec<T>>>>) {
         let old_len = self.cur_len;
         self.data = view;
-        self.cur_len = 0;
-        /*
+        let new_len =
             if let Some(data) = self.data.as_ref() {
                 data.read().unwrap().len()
             } else {
                 0
             };
-*/
-        self.cast.notify_each(0 .. std::cmp::max(old_len, self.cur_len));
+
+        self.cur_len = new_len;
+        self.cast.notify_each(0 .. std::cmp::max(old_len, new_len));
     }
 
     fn notify(&mut self, diff: &VecDiff<T>) {