Fix NPE when using broadcast as players are joining

patches/server/Adventure.patch

@@ -2241,6 +2241,7 @@ index 0000000000000000000000000000000000000000..00000000000000000000000000000000
 +
 +    @Override
 +    public void sendMessage(final net.kyori.adventure.identity.Identity identity, final net.kyori.adventure.text.Component message, final net.kyori.adventure.audience.MessageType type) {
++        if (getHandle().connection == null) return;
 +        final ClientboundChatPacket packet = new ClientboundChatPacket(null, type == net.kyori.adventure.audience.MessageType.CHAT ? net.minecraft.network.chat.ChatType.CHAT : net.minecraft.network.chat.ChatType.SYSTEM, identity.uuid());
 +        packet.adventure$message = message;
 +        this.getHandle().connection.send(packet);