Add note about why it's added

bungee/src/main/java/org/geysermc/floodgate/inject/bungee/BungeeInjector.java

@@ -91,6 +91,7 @@ public void inject() {
             ChannelInitializer<Channel> wrapper = new ChannelInitializer<Channel>() {
                 @Override
                 protected void initChannel(Channel channel) {
+                    // Check if the channel is open, see #547
                     if (!channel.isOpen()) {
                         return;
                     }