Fix warnings in tools/tiff2pcd.cpp
Fix warnings in tools/tiff2pcd.cpp

> tiff2pcd.cpp:356:24: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare]

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