readline: fix performance issue when large line
readline: fix performance issue when large line

Only run lineEnding.test() on the newly acquired chunk of string instead
of on the entire line buffer.

Reviewed-by: Trevor Norris <9cb5491eb5770dd8e0bf77a8a0335abf5f0488c5@gmail.com>

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