Add assert.equal for length of Buffer.concat(list, length)

[JacksonTian]

• Version: all
• Platform: all
• Subsystem: buffer

I don't know why/when user pass into invalid length. Hope to get more points for it.

[cjihrig]

Is your question why this returns an empty buffer instead of throwing:

const buf = Buffer.concat([Buffer.from('abc'), Buffer.from('def')], 'xyz');

Or why this automatically truncates instead of throwing:

Buffer.concat([Buffer.from('abc'), Buffer.from('def')], 1)

Or something else?

[JacksonTian]

Thanks, @cjihrig . That's my point.