duplicate failed urls are added into failedURLs
duplicate failed urls are added into failedURLs

fix bug when download image with option SDWebImageRetryFailed
ramoslin02/SDWebImage,D-cocoa/SDWebImage,dreampiggy/SDWebImage,heroims/SDWebImage,once00/SDWebImage,awkward/SDWebImage,matti-h121/SDWebImage,WeizeYu/SDWebImage,Meeca/SDWebImage,rongl/SDWebImage,j364960953/SDWebImage,wmed/SDWebImage,bwised/SDWebImage,iostalks/SDWebImage,AzenXu/SDWebImage,irealme/SDWebImage,zongmumask/SDWebImage,coderGHubL/SDWebImage,wantedly/SDWebImage,yuanhoujun/SDWebImage,balaprasanna/SDWebImage,malandiwang/SDWebImage,zhaofeiyan/SDWebImage,ioshger0125/SDWebImage,bpoplauschi/SDWebImage,smyrgl/SDWebImage,StoneLeon/SDWebImage,tempbottle/SDWebImage,MrLoong/SDWebImage,King-of-Monkey/SDWebImage,OnTheWay1988/SDWebImage,renssies/SDWebImage,CoderJFCK/SDWebImage,weiqiangqi/SDWebImage,NiuMengFei/SDWebImage,kalsariyac/SDWebImage,sujeking/SDWebImage,smartscreensoftware/SDWebImage,mokey1422/SDWebImage,wangmy/SDWebImage,igroomgrim/SDWebImage,mattjgalloway/SDWebImage,Derek316x/SDWebImage,yaoxiaoyong/SDWebImage,Chren/SDWebImage,HelloZhu/SDWebImage,ShunzhiTang/SDWebImage,rainkong/SDWebImage,myell0w/SDWebImage,luwu121/SDWebImage,Dcardcc/SDWebImage,princegoyal1987/SDWebImage,nickhingston/SDWebImage,Kekanto/SDWebImage,KuPai32G/SDWebImage,VrasidasP/SDWebImage_Test,ackerman123/SDWebImage,tokorom/SDWebImage,dcaunt/SDWebImage,dreampiggy/SDWebImage,TerryAsh/SDWebImage,SampleLiao/SDWebImage,JohnJin007/SDWebImage,mrchenhao/SDWebImage,CNMrGoat/SDWebImage,dpettigrew/SDWebImage,ikesyo/SDWebImage,zllbird/SDWebImage,cogddo/SDWebImage,Coeur/SDWebImage,muer2000/SDWebImage,NghiaTranUIT/SDWebImage,Kevin775263419/SDWebImage,bespider/SDWebImage,keslcod/SDWebImage,bhlzlx/SDWebImage,XuXiaoJunChina/SDWebImage,HSFGitHub/SDWebImage,elancom/SDWebImage,altrooz/SDWebImage,ymsheng/SDWebImage,GuitarPlayer-Ma/SDWebImage,xzenon/SDWebImage,donholly/SDWebImage,zakkhoyt/SDWebImage,Alsen007/SDWebImage,takeshineshiro/SDWebImage,initlifeinc/SDWebImage,wangpengfei1986/SDWebImage,Pingco/SDWebImage,ClassSix/SDWebImage,Eveian/SDWebImage,sdonly/SDWebImage,bgerstle/SDWebImage,wlsx/SDWebImage,Insfgg99x/SDWebImage,arnaudWasappli/SDWebImage,dahuilang1226/SDWebImage,howandhao/SDWebImage,SanjoDeundiak/SDWebImage,ywzw2013/SDWebImage,zhzenghui/SDWebImage,megawina/SDWebImage,wang2code/SDWebImage,vincnetdu/SDWebImage,flovilmart/SDWebImage,chenhong/SDWebImage,adrianmacneil/SDWebImage,iMinichrispy/SDWebImage,gemwulee/SDWebImage,bb-coder/SDWebImage,wpstarnice/SDWebImage,zh-se/SDWebImage,809848367/SDWebImage,iSqXIE/SDWebImage,DevSonw/SDWebImage,jackywpy/SDWebImage,dachaoisme/SDWebImage,iosnatarajan/SDWebImage,Gaantz/SDWebImage,sandyway/SDWebImage,tangShunZhi/SDWebImage,zhang-yawei/SDWebImage,aefly/SDWebImage,harishkashyap/SDWebImage,buleSky111/SDWebImage,johnmyqin/SDWebImage,leelili/SDWebImage,fuzhiqiang1989/SDWebImage,coderShao/SDWebImage,LGLee/SDWebImage,fcx891231/SDWebImage,sarah89lee/SDWebImage,maominghui/SDWebImage,jiisd/SDWebImage,sunzeboy/SDWebImage,kostassite/SDWebImage,cochat/SDWebImage,awkward/SDWebImage,280482431/SDWebImage,yunzhongyoulong/SDWebImage,623049115/SDWebImage,wuxsoft/SDWebImage,HannaLu/SDWebImage,TrainingPair/SDWebImage,brasbug/SDWebImage,Dongyafeiying/SDWebImage,caoer/SDWebImage,Harvey4431/SDWebImage,odyth/SDWebImage,zhenxingliu/SDWebImage,kjiwu/SDWebImage,kimiWu/SDWebImage,Monk428/SDWebImage,ttgb/SDWebImage,ForrestAlfred/SDWebImage,timkoma/SDWebImage,xswm1123/SDWebImage,d191562687/SDWebImage,imjerrybao/SDWebImage,Kingside/SDWebImage,yyMlv/SDWebImage,PodRepo/SDWebImage,zhuzhengwei/SDWebImage,masterfego/SDWebImage,Dcard/SDWebImage,dreampiggy/SDWebImage,Deyine/SDWebImage,awkward/SDWebImage,nuorder/SDWebImage,shifujun/SDWebImage,zilaiyedaren/SDWebImage,raopc/SDWebImage,amyhametov/SDWebImage,KeyJohn/SDWebImage,zhang-yawei/ZYWSDWebImage,mayazhe/SDWebImage,jianguozhang/SDWebImage,twobitlabs/SDWebImage,bhumi19/HelloWorld,Frntbac/SDWebImage,SureEdding/SDWebImage,seyfeddin/SDWebImage,yingongzheng123/SDWebImage,nickcheng/SDWebImage,ruaho/SDWebImage,GaryJuan/SDWebImage,wenxp/SDWebImage,doubleencore/SDWebImage,wanglj7525/SDWebImage,ferrior30/SDWebImage,tualatrix/SDWebImage,qingsong-xu/SDWebImage,klundberg/SDWebImage,wentaozone/SDWebImage,SummerHF/SDWebImage,goodheart/SDWebImage,rayshen/SDWebImage,xianzhiliao/SDWebImage,izackp/SDWebImage,Jesee-jia/SDWebImage,smule/SDWebImage,iheartradio/SDWebImage,xiuxiuing/SDWebImage,rs/SDWebImage,littledogboy/SDWebImage,Stubborn-Geek/SDWebImage,geoffmacd/SDWebImage,rsidorakin/SDWebImage,inbilin-inc/SDWebImage