fix: Crash on uninitialized filterManager

Not sure if this will only hide the root cause because the proper flow on pairing is unknown to me. But from what I've seen Waku is only started after login. While `subscribe` and `unsubscribe` is used in the pairing flow as well.

Author: alexjba

messaging/waku/gowaku.go

@@ -968,6 +968,9 @@ func (w *Waku) subscribe(f *common.Filter) (string, error) {
 	}
 
 	if w.cfg.LightClient {
+		if w.filterManager == nil {
+			return id, nil
+		}
 		cf := protocol.NewContentFilter(f.PubsubTopic, f.ContentTopics.ContentTopics()...)
 		w.filterManager.SubscribeFilter(id, cf)
 	}
@@ -983,6 +986,9 @@ func (w *Waku) Unsubscribe(ctx context.Context, id string) error {
 	}
 
 	if w.cfg.LightClient {
+        if w.filterManager == nil {
+            return nil
+        }
 		w.filterManager.UnsubscribeFilter(id)
 	}