`readVarLong` returns incorrect result for large values

[Johni0702]

Someone probably copy/pasted the readVarInt code and forgot to change the value type from int to long.

PacketLib/src/main/java/com/github/steveice10/packetlib/codec/BasePacketCodecHelper.java

Lines 129 to 130 in e21e6c4

	public long readVarLong(ByteBuf buf) {
	int value = 0;