Don't forward chat acknowledgement if the client didn't acknowledge any chat

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/LastSeenMessages.java

@@ -52,10 +52,6 @@ public class LastSeenMessages {
     buf.writeBytes(Arrays.copyOf(acknowledged.toByteArray(), DIV_FLOOR));
   }
 
-  public boolean isEmpty() {
-    return acknowledged.isEmpty();
-  }
-
   public int getOffset() {
     return this.offset;
   }

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/session/SessionCommandHandler.java

@@ -60,7 +60,11 @@ public class SessionCommandHandler implements CommandHandler<SessionPlayerComman
     }
     // An unsigned command with a 'last seen' update will not happen as of 1.20.5+, but for earlier versions - we still
     // need to pass through the acknowledgement
-    return new ChatAcknowledgementPacket(packet.lastSeenMessages.getOffset());
+    final int offset = packet.lastSeenMessages.getOffset();
+    if (offset != 0) {
+      return new ChatAcknowledgementPacket(offset);
+    }
+    return null;
   }
 
   @Nullable