util-core: optimize StringCoder.unapply
util-core: optimize StringCoder.unapply

Problem / Solution

String decoding of Bufs can be faster and cheaper.

RB_ID=898382

twitter/util,BuoyantIO/twitter-util,twitter/util,BuoyantIO/twitter-util,BuoyantIO/twitter-util,twitter/util,BuoyantIO/twitter-util