Fix warnings in common/io.hpp
Fix warnings in common/io.hpp

> io.hpp:275:30: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]

sbec/pcl,soulsheng/pcl,damienjadeduff/pcl,nh2/pcl,pkuhto/pcl,chatchavan/pcl,soulsheng/pcl,KevenRing/vlp,stefanbuettner/pcl,lydhr/pcl,MMiknis/pcl,kanster/pcl,stfuchs/pcl,kanster/pcl,3dtof/pcl,shivmalhotra/pcl,cascheberg/pcl,DaikiMaekawa/pcl,lebronzhang/pcl,MMiknis/pcl,mikhail-matrosov/pcl,soulsheng/pcl,KevenRing/vlp,nh2/pcl,mschoeler/pcl,shivmalhotra/pcl,DaikiMaekawa/pcl,3dtof/pcl,krips89/pcl_newfeatures,chenxingzhe/pcl,KevenRing/vlp,soulsheng/pcl,pkuhto/pcl,starius/pcl,lydhr/pcl,soulsheng/pcl,Tabjones/pcl,krips89/pcl_newfeatures,sbec/pcl,Tabjones/pcl,shivmalhotra/pcl,chatchavan/pcl,3dtof/pcl,3dtof/pcl,stfuchs/pcl,ipa-rmb/pcl,KevenRing/vlp,shyamalschandra/pcl,KevenRing/pcl,stfuchs/pcl,fanxiaochen/mypcltest,chenxingzhe/pcl,MMiknis/pcl,shyamalschandra/pcl,nikste/pcl,closerbibi/pcl,cascheberg/pcl,shivmalhotra/pcl,3dtof/pcl,the-glu/pcl,krips89/pcl_newfeatures,msalvato/pcl_kinfu_highres,chenxingzhe/pcl,lebronzhang/pcl,msalvato/pcl_kinfu_highres,drmateo/pcl,the-glu/pcl,chatchavan/pcl,KevenRing/vlp,stefanbuettner/pcl,damienjadeduff/pcl,msalvato/pcl_kinfu_highres,v4hn/pcl,chenxingzhe/pcl,fskuka/pcl,fskuka/pcl,ResByte/pcl,mikhail-matrosov/pcl,fanxiaochen/mypcltest,raydtang/pcl,mschoeler/pcl,wgapl/pcl,pkuhto/pcl,jakobwilm/pcl,srbhprajapati/pcl,shyamalschandra/pcl,starius/pcl,KevenRing/pcl,closerbibi/pcl,starius/pcl,Tabjones/pcl,shivmalhotra/pcl,raydtang/pcl,mschoeler/pcl,ipa-rmb/pcl,the-glu/pcl,v4hn/pcl,MMiknis/pcl,wgapl/pcl,lebronzhang/pcl,nikste/pcl,zavataafnan/pcl-truck,RufaelDev/pcc-mp3dg,zavataafnan/pcl-truck,locnx1984/pcl,v4hn/pcl,drmateo/pcl,chatchavan/pcl,fskuka/pcl,shangwuhencc/pcl,fanxiaochen/mypcltest,closerbibi/pcl,zhangxaochen/pcl,cascheberg/pcl,msalvato/pcl_kinfu_highres,simonleonard/pcl,shangwuhencc/pcl,raydtang/pcl,srbhprajapati/pcl,fskuka/pcl,jeppewalther/kinfu_segmentation,jakobwilm/pcl,LZRS/pcl,jakobwilm/pcl,stefanbuettner/pcl,damienjadeduff/pcl,mschoeler/pcl,the-glu/pcl,mikhail-matrosov/pcl,raydtang/pcl,Tabjones/pcl,stefanbuettner/pcl,RufaelDev/pcc-mp3dg,closerbibi/pcl,ResByte/pcl,stefanbuettner/pcl,shangwuhencc/pcl,lydhr/pcl,srbhprajapati/pcl,mikhail-matrosov/pcl,locnx1984/pcl,drmateo/pcl,cascheberg/pcl,jakobwilm/pcl,raydtang/pcl,damienjadeduff/pcl,stfuchs/pcl,jakobwilm/pcl,stfuchs/pcl,nikste/pcl,ResByte/pcl,DaikiMaekawa/pcl,MMiknis/pcl,srbhprajapati/pcl,LZRS/pcl,locnx1984/pcl,wgapl/pcl,krips89/pcl_newfeatures,KevenRing/pcl,zhangxaochen/pcl,msalvato/pcl_kinfu_highres,lydhr/pcl,chenxingzhe/pcl,lebronzhang/pcl,RufaelDev/pcc-mp3dg,kanster/pcl,DaikiMaekawa/pcl,zhangxaochen/pcl,drmateo/pcl,shyamalschandra/pcl,KevenRing/pcl,locnx1984/pcl,LZRS/pcl,nh2/pcl,kanster/pcl,ipa-rmb/pcl,ResByte/pcl,starius/pcl,shyamalschandra/pcl,cascheberg/pcl,KevenRing/pcl,ResByte/pcl,wgapl/pcl,ipa-rmb/pcl,pkuhto/pcl,shangwuhencc/pcl,shangwuhencc/pcl,fskuka/pcl,the-glu/pcl,starius/pcl,fanxiaochen/mypcltest,kanster/pcl,fanxiaochen/mypcltest,krips89/pcl_newfeatures,zavataafnan/pcl-truck,sbec/pcl,nikste/pcl,mikhail-matrosov/pcl,simonleonard/pcl,ipa-rmb/pcl,sbec/pcl,simonleonard/pcl,zavataafnan/pcl-truck,lydhr/pcl,drmateo/pcl,srbhprajapati/pcl,v4hn/pcl,DaikiMaekawa/pcl,jeppewalther/kinfu_segmentation,zhangxaochen/pcl,zavataafnan/pcl-truck,jeppewalther/kinfu_segmentation,lebronzhang/pcl,damienjadeduff/pcl,simonleonard/pcl,jeppewalther/kinfu_segmentation,nh2/pcl,locnx1984/pcl,mschoeler/pcl,nikste/pcl,closerbibi/pcl,sbec/pcl,simonleonard/pcl,pkuhto/pcl,LZRS/pcl,Tabjones/pcl,zhangxaochen/pcl,RufaelDev/pcc-mp3dg,v4hn/pcl,RufaelDev/pcc-mp3dg,jeppewalther/kinfu_segmentation,wgapl/pcl,LZRS/pcl