protocols/gossipsub: Update topic_peers (#2325)

Co-authored-by: Max Inden <mail@max-inden.de>

protocols/gossipsub/CHANGELOG.md

@@ -1,8 +1,11 @@
 # 0.33.1 [unreleased]
 
+- Fix bug in internal peer's topics tracking (see [PR 2325]).
+
 - Use `instant` and `futures-timer` instead of `wasm-timer` (see [PR 2245]).
 
 [PR 2245]: https://github.com/libp2p/rust-libp2p/pull/2245
+[PR 2325]: https://github.com/libp2p/rust-libp2p/pull/2325
 
 # 0.33.0 [2021-11-01]
 

protocols/gossipsub/src/behaviour.rs

@@ -1252,6 +1252,10 @@ where
                 .entry(*peer_id)
                 .or_default()
                 .insert(topic.clone());
+            self.topic_peers
+                .entry(topic.clone())
+                .or_default()
+                .insert(*peer_id);
         }
 
         // we don't GRAFT to/from explicit peers; complain loudly if this happens