fixed a bug in btree
fixed a bug in btree

lanbing510/Algorithms,switchkiller/algorithms,noname007/algorithms,fw1121/algorithms,noname007/algorithms,qvex/algorithms,dumubuchenglin/algorithms,tempbottle/algorithms,greyg00s/algorithms,lanbing510/Algorithms,allengaller/algorithms,fw1121/algorithms,dumubuchenglin/algorithms,NoSmartNoMan/algorithms,jacklicn/algorithms,fengzhyuan/algorithms,xmfbit/algorithms,sigma-random/algorithms,ashwini0529/algorithms-1,NoSmartNoMan/algorithms,hengwusanren/algorithms,ashwini0529/algorithms-1,hengwusanren/algorithms,M4573R/algorithms-1,shijiaxing/algorithms,shijiaxing/algorithms,fengzhyuan/algorithms,M4573R/algorithms-1,xtaci/algorithms,greyg00s/algorithms,xtaci/algorithms,tempbottle/algorithms,allengaller/algorithms,zhenglaizhang/algorithms,zhenglaizhang/algorithms,qvex/algorithms,jacklicn/algorithms,sigma-random/algorithms,switchkiller/algorithms,xmfbit/algorithms