db/version_set.cc: remove unnecessary checks
db/version_set.cc: remove unnecessary checks

Fix for:

[db/version_set.cc:1219]: (style) Unsigned variable 'last_file'
 can't be negative so it is unnecessary to test it.
[db/version_set.cc:1234]: (style) Unsigned variable 'first_file'
 can't be negative so it is unnecessary to test it.

Signed-off-by: Danny Al-Gaaf <473e39ac77cf392f0dd9bacde8409de76c14d006@bisect.de>

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