peer: fix race condition - open emitted after peer.close().

lib/net/peer.js

@@ -290,6 +290,12 @@ Peer.prototype.open = co(function* open() {
     return;
   }
 
+  // The peer may have been killed before
+  // the handshake finished. In this case,
+  // do not emit `open`.
+  if (this.destroyed)
+    return;
+
   // Finally we can let the pool know
   // that this peer is ready to go.
   this.emit('open');