stream_wrap: remove superfluous buffer len check
stream_wrap: remove superfluous buffer len check

It's a buffer so it's never bigger than Buffer::kMaxLength bytes,
which in turn is always < INT_MAX.

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node