Fix comparison between signed and usigned integers
Fix comparison between signed and usigned integers

Summary: Not sure why this fails on some compilers and doesn't on others.

Test Plan: none

Reviewers: meyering, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38673

temicai/rocksdb,zhangpng/rocksdb,temicai/rocksdb,mbarbon/rocksdb,caijieming-baidu/rocksdb,makelivedotnet/rocksdb,mbarbon/rocksdb,hobinyoon/rocksdb,wenduo/rocksdb,norton/rocksdb,Applied-Duality/rocksdb,JohnPJenkins/rocksdb,mbarbon/rocksdb,tizzybec/rocksdb,JoeWoo/rocksdb,alihalabyah/rocksdb,Vaisman/rocksdb,wenduo/rocksdb,wskplho/rocksdb,caijieming-baidu/rocksdb,wenduo/rocksdb,mbarbon/rocksdb,ylong/rocksdb,fengshao0907/rocksdb,zhangpng/rocksdb,IMCG/RcoksDB,lgscofield/rocksdb,ryneli/rocksdb,luckywhu/rocksdb,rDSN-Projects/rocksdb.replicated,SunguckLee/RocksDB,norton/rocksdb,SunguckLee/RocksDB,wat-ze-hex/rocksdb,Applied-Duality/rocksdb,tizzybec/rocksdb,caijieming-baidu/rocksdb,makelivedotnet/rocksdb,dkorolev/rocksdb,bbiao/rocksdb,ylong/rocksdb,RyanTech/rocksdb,wskplho/rocksdb,wskplho/rocksdb,wat-ze-hex/rocksdb,Applied-Duality/rocksdb,Andymic/rocksdb,geraldoandradee/rocksdb,JoeWoo/rocksdb,temicai/rocksdb,temicai/rocksdb,makelivedotnet/rocksdb,vmx/rocksdb,flabby/rocksdb,jalexanderqed/rocksdb,sorphi/rocksdb,RyanTech/rocksdb,geraldoandradee/rocksdb,fengshao0907/rocksdb,flabby/rocksdb,kaschaeffer/rocksdb,jalexanderqed/rocksdb,OverlordQ/rocksdb,lgscofield/rocksdb,flabby/rocksdb,norton/rocksdb,kaschaeffer/rocksdb,kaschaeffer/rocksdb,jalexanderqed/rocksdb,fengshao0907/rocksdb,IMCG/RcoksDB,geraldoandradee/rocksdb,ylong/rocksdb,luckywhu/rocksdb,ylong/rocksdb,vmx/rocksdb,norton/rocksdb,alihalabyah/rocksdb,anagav/rocksdb,wlqGit/rocksdb,wenduo/rocksdb,norton/rocksdb,anagav/rocksdb,JohnPJenkins/rocksdb,wlqGit/rocksdb,tsheasha/rocksdb,siddhartharay007/rocksdb,facebook/rocksdb,lgscofield/rocksdb,zhangpng/rocksdb,facebook/rocksdb,Andymic/rocksdb,makelivedotnet/rocksdb,bbiao/rocksdb,fengshao0907/rocksdb,siddhartharay007/rocksdb,luckywhu/rocksdb,ryneli/rocksdb,lgscofield/rocksdb,hobinyoon/rocksdb,vmx/rocksdb,zhangpng/rocksdb,JackLian/rocksdb,Applied-Duality/rocksdb,JohnPJenkins/rocksdb,facebook/rocksdb,biddyweb/rocksdb,Vaisman/rocksdb,skunkwerks/rocksdb,geraldoandradee/rocksdb,flabby/rocksdb,JackLian/rocksdb,Andymic/rocksdb,skunkwerks/rocksdb,vmx/rocksdb,alihalabyah/rocksdb,sorphi/rocksdb,fengshao0907/rocksdb,vashstorm/rocksdb,dkorolev/rocksdb,siddhartharay007/rocksdb,dkorolev/rocksdb,bbiao/rocksdb,RyanTech/rocksdb,JohnPJenkins/rocksdb,alihalabyah/rocksdb,RyanTech/rocksdb,facebook/rocksdb,alihalabyah/rocksdb,wenduo/rocksdb,hobinyoon/rocksdb,kaschaeffer/rocksdb,tizzybec/rocksdb,geraldoandradee/rocksdb,Vaisman/rocksdb,vmx/rocksdb,lgscofield/rocksdb,bbiao/rocksdb,JoeWoo/rocksdb,JoeWoo/rocksdb,vashstorm/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,tizzybec/rocksdb,mbarbon/rocksdb,luckywhu/rocksdb,RyanTech/rocksdb,Applied-Duality/rocksdb,JoeWoo/rocksdb,dkorolev/rocksdb,tizzybec/rocksdb,JohnPJenkins/rocksdb,jalexanderqed/rocksdb,biddyweb/rocksdb,JackLian/rocksdb,ylong/rocksdb,sorphi/rocksdb,luckywhu/rocksdb,wskplho/rocksdb,bbiao/rocksdb,flabby/rocksdb,JackLian/rocksdb,Andymic/rocksdb,kaschaeffer/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,anagav/rocksdb,wskplho/rocksdb,biddyweb/rocksdb,flabby/rocksdb,facebook/rocksdb,bbiao/rocksdb,wlqGit/rocksdb,wlqGit/rocksdb,tizzybec/rocksdb,caijieming-baidu/rocksdb,wat-ze-hex/rocksdb,Vaisman/rocksdb,rDSN-Projects/rocksdb.replicated,wlqGit/rocksdb,vashstorm/rocksdb,wat-ze-hex/rocksdb,wskplho/rocksdb,ryneli/rocksdb,hobinyoon/rocksdb,fengshao0907/rocksdb,siddhartharay007/rocksdb,vmx/rocksdb,Vaisman/rocksdb,zhangpng/rocksdb,SunguckLee/RocksDB,vashstorm/rocksdb,temicai/rocksdb,geraldoandradee/rocksdb,dkorolev/rocksdb,OverlordQ/rocksdb,luckywhu/rocksdb,lgscofield/rocksdb,RyanTech/rocksdb,IMCG/RcoksDB,flabby/rocksdb,wskplho/rocksdb,ryneli/rocksdb,makelivedotnet/rocksdb,rDSN-Projects/rocksdb.replicated,wlqGit/rocksdb,OverlordQ/rocksdb,IMCG/RcoksDB,OverlordQ/rocksdb,makelivedotnet/rocksdb,tsheasha/rocksdb,kaschaeffer/rocksdb,norton/rocksdb,tsheasha/rocksdb,SunguckLee/RocksDB,JoeWoo/rocksdb,fengshao0907/rocksdb,OverlordQ/rocksdb,tsheasha/rocksdb,mbarbon/rocksdb,skunkwerks/rocksdb,dkorolev/rocksdb,rDSN-Projects/rocksdb.replicated,SunguckLee/RocksDB,luckywhu/rocksdb,alihalabyah/rocksdb,JackLian/rocksdb,hobinyoon/rocksdb,JohnPJenkins/rocksdb,hobinyoon/rocksdb,tizzybec/rocksdb,rDSN-Projects/rocksdb.replicated,Applied-Duality/rocksdb,SunguckLee/RocksDB,biddyweb/rocksdb,skunkwerks/rocksdb,vmx/rocksdb,biddyweb/rocksdb,siddhartharay007/rocksdb,jalexanderqed/rocksdb,jalexanderqed/rocksdb,wlqGit/rocksdb,anagav/rocksdb,temicai/rocksdb,JackLian/rocksdb,biddyweb/rocksdb,norton/rocksdb,bbiao/rocksdb,SunguckLee/RocksDB,skunkwerks/rocksdb,rDSN-Projects/rocksdb.replicated,alihalabyah/rocksdb,rDSN-Projects/rocksdb.replicated,Andymic/rocksdb,sorphi/rocksdb,biddyweb/rocksdb,temicai/rocksdb,IMCG/RcoksDB,anagav/rocksdb,facebook/rocksdb,ylong/rocksdb,mbarbon/rocksdb,zhangpng/rocksdb,caijieming-baidu/rocksdb,facebook/rocksdb,skunkwerks/rocksdb,caijieming-baidu/rocksdb,makelivedotnet/rocksdb,wat-ze-hex/rocksdb,sorphi/rocksdb,SunguckLee/RocksDB,Andymic/rocksdb,dkorolev/rocksdb,zhangpng/rocksdb,siddhartharay007/rocksdb,tsheasha/rocksdb,Vaisman/rocksdb,IMCG/RcoksDB,JackLian/rocksdb,RyanTech/rocksdb,hobinyoon/rocksdb,jalexanderqed/rocksdb,tsheasha/rocksdb,wenduo/rocksdb,sorphi/rocksdb,ylong/rocksdb,Andymic/rocksdb,wat-ze-hex/rocksdb,bbiao/rocksdb,ryneli/rocksdb,norton/rocksdb,wenduo/rocksdb,wenduo/rocksdb,OverlordQ/rocksdb,anagav/rocksdb,skunkwerks/rocksdb,geraldoandradee/rocksdb,JoeWoo/rocksdb,OverlordQ/rocksdb,JohnPJenkins/rocksdb,siddhartharay007/rocksdb,lgscofield/rocksdb,vashstorm/rocksdb,IMCG/RcoksDB,wat-ze-hex/rocksdb,anagav/rocksdb,kaschaeffer/rocksdb,tsheasha/rocksdb,facebook/rocksdb,sorphi/rocksdb,caijieming-baidu/rocksdb,ryneli/rocksdb,vashstorm/rocksdb,vashstorm/rocksdb,vmx/rocksdb,Applied-Duality/rocksdb,Vaisman/rocksdb,tsheasha/rocksdb