Fix v0.4.x race condition
Fix v0.4.x race condition

Node v0.4.x sometimes seems to emit a data event were the buffer is
undefined.

See: http://travis-ci.org/#!/felixge/node-mysql/jobs/1849436

This patch simplifies the parser code and handles this problem.

l371559739/node-mysql,XiaoLongW/node-mysql,ashwinks/node-mysql,Jimbly/node-mysql,yulongge/node-mysql,lukw00/node-mysql,teng2015/node-mysql,seangarner/node-mysql,WY08271/node-mysql,mhasan3/node-mysql,AndersonGitHub/node-mysql,bORm/node-mysql,yourcaptain/node-mysql,wxkdesky/node-mysql,saisai/node-mysql,danidomi/node-mysql,AshWilliams/node-mysql,bbito/node-mysql,apathyjade/node-mysql,NikosEfthias/node-mysql,1602/node-mysql,chinazhaghai/node-mysql,felixge/node-mysql,cgvarela/node-mysql,grooverdan/node-mysql,yanninho/node-mysql,mysqljs/mysql,linalu1/node-mysql,tempbottle/node-mysql,shipci/node-mysql,theblackperl/node-mysql,acorbi/node-mysql,yan5845hao/node-mysql-1,zhhb/node-mysql