Fix warnings in apps/ni_agast.cpp
Fix warnings in apps/ni_agast.cpp

> ni_agast.cpp:233:13: warning: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Wsign-compare]

3dtof/pcl,DaikiMaekawa/pcl,soulsheng/pcl,RufaelDev/pcc-mp3dg,drmateo/pcl,KevenRing/vlp,damienjadeduff/pcl,damienjadeduff/pcl,ipa-rmb/pcl,kanster/pcl,cascheberg/pcl,closerbibi/pcl,Tabjones/pcl,mikhail-matrosov/pcl,cascheberg/pcl,KevenRing/pcl,DaikiMaekawa/pcl,starius/pcl,LZRS/pcl,drmateo/pcl,MMiknis/pcl,starius/pcl,the-glu/pcl,fanxiaochen/mypcltest,MMiknis/pcl,damienjadeduff/pcl,sbec/pcl,stefanbuettner/pcl,fskuka/pcl,sbec/pcl,nikste/pcl,starius/pcl,krips89/pcl_newfeatures,mschoeler/pcl,chenxingzhe/pcl,RufaelDev/pcc-mp3dg,fskuka/pcl,the-glu/pcl,shyamalschandra/pcl,LZRS/pcl,lebronzhang/pcl,kanster/pcl,damienjadeduff/pcl,RufaelDev/pcc-mp3dg,shivmalhotra/pcl,stefanbuettner/pcl,lebronzhang/pcl,shyamalschandra/pcl,the-glu/pcl,pkuhto/pcl,mschoeler/pcl,simonleonard/pcl,DaikiMaekawa/pcl,lydhr/pcl,krips89/pcl_newfeatures,closerbibi/pcl,stfuchs/pcl,mschoeler/pcl,pkuhto/pcl,locnx1984/pcl,ResByte/pcl,simonleonard/pcl,chenxingzhe/pcl,the-glu/pcl,nikste/pcl,fanxiaochen/mypcltest,shangwuhencc/pcl,kanster/pcl,shivmalhotra/pcl,drmateo/pcl,3dtof/pcl,closerbibi/pcl,pkuhto/pcl,mikhail-matrosov/pcl,KevenRing/pcl,wgapl/pcl,shangwuhencc/pcl,raydtang/pcl,LZRS/pcl,fanxiaochen/mypcltest,fanxiaochen/mypcltest,ResByte/pcl,locnx1984/pcl,zhangxaochen/pcl,stefanbuettner/pcl,mikhail-matrosov/pcl,wgapl/pcl,RufaelDev/pcc-mp3dg,Tabjones/pcl,3dtof/pcl,LZRS/pcl,3dtof/pcl,shangwuhencc/pcl,drmateo/pcl,lydhr/pcl,stefanbuettner/pcl,lydhr/pcl,MMiknis/pcl,MMiknis/pcl,mschoeler/pcl,fanxiaochen/mypcltest,wgapl/pcl,starius/pcl,cascheberg/pcl,lydhr/pcl,lebronzhang/pcl,zhangxaochen/pcl,closerbibi/pcl,raydtang/pcl,nikste/pcl,fskuka/pcl,krips89/pcl_newfeatures,lebronzhang/pcl,locnx1984/pcl,ipa-rmb/pcl,KevenRing/vlp,ipa-rmb/pcl,soulsheng/pcl,mikhail-matrosov/pcl,fskuka/pcl,ResByte/pcl,shangwuhencc/pcl,soulsheng/pcl,shivmalhotra/pcl,cascheberg/pcl,mikhail-matrosov/pcl,KevenRing/pcl,simonleonard/pcl,drmateo/pcl,zhangxaochen/pcl,soulsheng/pcl,soulsheng/pcl,locnx1984/pcl,nikste/pcl,ipa-rmb/pcl,cascheberg/pcl,kanster/pcl,sbec/pcl,shivmalhotra/pcl,Tabjones/pcl,stfuchs/pcl,simonleonard/pcl,mschoeler/pcl,raydtang/pcl,lydhr/pcl,KevenRing/vlp,krips89/pcl_newfeatures,wgapl/pcl,the-glu/pcl,nikste/pcl,LZRS/pcl,lebronzhang/pcl,MMiknis/pcl,DaikiMaekawa/pcl,starius/pcl,KevenRing/vlp,KevenRing/pcl,closerbibi/pcl,shyamalschandra/pcl,stfuchs/pcl,simonleonard/pcl,ipa-rmb/pcl,shangwuhencc/pcl,ResByte/pcl,pkuhto/pcl,KevenRing/pcl,raydtang/pcl,ResByte/pcl,Tabjones/pcl,KevenRing/vlp,zhangxaochen/pcl,Tabjones/pcl,3dtof/pcl,chenxingzhe/pcl,pkuhto/pcl,chenxingzhe/pcl,DaikiMaekawa/pcl,damienjadeduff/pcl,stfuchs/pcl,shivmalhotra/pcl,sbec/pcl,shyamalschandra/pcl,locnx1984/pcl,stfuchs/pcl,wgapl/pcl,krips89/pcl_newfeatures,shyamalschandra/pcl,kanster/pcl,RufaelDev/pcc-mp3dg,fskuka/pcl,raydtang/pcl,chenxingzhe/pcl,zhangxaochen/pcl,stefanbuettner/pcl,sbec/pcl