Close one last "proxy crasher" loophole

proxy/src/main/java/com/velocitypowered/proxy/connection/MinecraftConnection.java

@@ -152,7 +152,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
         }
       }
 
-      ctx.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
+      installDiscardHandler(ctx);
       ctx.close();
     }
   }
@@ -168,6 +168,14 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
     Preconditions.checkState(this.channel.eventLoop().inEventLoop(), "Not in event loop");
   }
 
+  private void installDiscardHandler(ChannelHandlerContext ctx) {
+    ctx.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
+  }
+
+  private void installDiscardHandler() {
+    channel.pipeline().addBefore(MINECRAFT_DECODER, "discard", DiscardHandler.HANDLER);
+  }
+
   public EventLoop eventLoop() {
     return channel.eventLoop();
   }
@@ -208,6 +216,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
   public void closeWith(Object msg) {
     if (channel.isActive()) {
       knownDisconnect = true;
+      installDiscardHandler();
       channel.writeAndFlush(msg).addListener(ChannelFutureListener.CLOSE);
     }
   }
@@ -217,6 +226,7 @@ public class MinecraftConnection extends ChannelInboundHandlerAdapter {
    */
   public void close() {
     if (channel.isActive()) {
+      installDiscardHandler();
       channel.close();
     }
   }