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

> io.hpp:406:25: warning: comparison of integers of different signs: 'int' and 'const uint32_t' (aka 'const unsigned int') [-Wsign-compare]
> io.hpp:433:29: warning: comparison of integers of different signs: 'int' and 'const uint32_t' (aka 'const unsigned int') [-Wsign-compare]
> io.hpp:476:27: warning: comparison of integers of different signs: 'int' and 'const uint32_t' (aka 'const unsigned int') [-Wsign-compare]

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