Optimise file session, if session data is empty and not changed, ignore flush
Optimise file session, if session data is empty and not changed, ignore flush

75team/thinkjs,75team/thinkjs,maxzhang/thinkjs,maxzhang/thinkjs,75team/thinkjs,Qihoo360/thinkjs,maxzhang/thinkjs,akira-cn/thinkjs,akira-cn/thinkjs,akira-cn/thinkjs,snadn/thinkjs,thinkjs/thinkjs