Client sending invalid button id for CPacketEnchantItem packet causes server side exception

The bug

The following is based on decompiled version of Minecraft 1.9 using MCP 9.24 beta. All method and class names are the names used in the decompiled version.

When the client sends an invalid button id in a CPacketEnchantItem packet the server prints an ArrayIndexOutOfBoundsException. This could be abused by constantly sending invalid packets and crashing the server.

How to reproduce (modded client)

Have for example the method net.minecraft.client.multiplayer.PlayerControllerMP.sendEnchantPacket(int, int) always send CPacketEnchantItem packets with -10 as button id