Verify buffer size before reading

[Nevon]

#11 was caused by attempting to read the offset and size from the buffer without checking that there were enough bytes in the buffer. The fix was to simply do that check first:

kafkajs/src/protocol/messageSet/decoder.js

Lines 68 to 74 in 01345c9

	if (!decoder.canReadInt64()) {
	throw new KafkaJSPartialMessageError(
	`Tried to decode a partial message: There isn't enough bytes to read the offset`
	)
	}
	const offset = decoder.readInt64().toString()

However, we don't want to have to do these checks manually everywhere we try to read from a buffer. We could check the buffer size in the decoder itself, but it doesn't have the knowledge about messages etc, so it would just be able to throw very generic errors.

The suggestion is to never use theDecoder directly, but rather create specific decoders for what we are trying to decode, for example MessageDecoder, which can call the primitive methods on the Decoder, catch the generic errors and re-throw more specific ones.

[Nevon]

This is probably not happening anytime soon. Closing for now.