Fixed a signed and unsigned comparison in Compaction
Fixed a signed and unsigned comparison in Compaction

Summary:
Fixed a signed and unsigned comparison in Compaction

Test Plan:
make db_test
export ROCKSDB_TESTS=Compaction
./db_test

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