if only line data exists and no other data, turn _deltaX to 1.0, just like what LineChartView did
if only line data exists and no other data, turn _deltaX to 1.0, just like what LineChartView did

jum/Charts,liuxuan30/Charts,summerlove57/ios-charts,MAARK/Charts,shujucn/ios-charts,GreenCom-Networks/ios-charts,icecrystal23/ios-charts,liuxuan30/Charts,mobistix/ios-charts,noais/ios-charts,liuxuan30/ios-charts,FreddyZeng/Charts,ekohe/ios-charts,StephenVinouze/ios-charts,boluomeng/Charts,jesseXu/Charts,duanhjlt/ios-charts,franqueli/ios-charts,danielgindi/Charts,koroff/Charts,liuxuan30/ios-charts,programming086/ios-charts,dtrauger/Charts,stardust139/ios-charts,FreddyZeng/Charts,liuxuan30/ios-charts,jesseXu/Charts,Shannon-s-Dreamland/Charts,hanquochan/Charts,MAARK/Charts,franqueli/ios-charts,gunterhager/ios-charts,hanquochan/Charts,parkboo/ios-charts,koroff/Charts,gunterhager/ios-charts,StephenVinouze/ios-charts,leoMehlig/Charts,SereivoanYong/Charts,leoMehlig/ios-charts,ConcepterDev/ios-charts,boluomeng/Charts,GreenCom-Networks/ios-charts,liuxuan30/Charts,SereivoanYong/Charts,Eflet/Charts,GreenCom-Networks/ios-charts,jjatie/Charts,danielgindi/Charts,dtrauger/Charts,franqueli/ios-charts,dtrauger/Charts,ekohe/ios-charts,zntfdr/ios-charts,smokyonion/ios-charts,leoMehlig/Charts,jjatie/Charts,programming086/ios-charts,ConcepterDev/ios-charts,danielgindi/ios-charts,gjpc/ios-charts,convergeeducacao/Charts,jjatie/Charts,jum/Charts,StephenVinouze/ios-charts,shujucn/ios-charts,leoMehlig/ios-charts,zntfdr/ios-charts,FreddyZeng/Charts,Eflet/Charts,boluomeng/Charts,koroff/Charts,FreddyZeng/Charts,leoMehlig/ios-charts,mobistix/ios-charts,Eflet/Charts,smokyonion/ios-charts,aelam/Charts,jum/Charts,danielgindi/Charts,zntfdr/ios-charts,leoMehlig/ios-charts,SBGMobile/Charts,danielgindi/Charts,StephenVinouze/ios-charts,LiveHappier/Charts,noais/ios-charts,icecrystal23/ios-charts,SereivoanYong/Charts,dtrauger/Charts,aelam/Charts,parkboo/ios-charts,ekohe/ios-charts,smokyonion/ios-charts,jesseXu/Charts,parkboo/ios-charts,convergeeducacao/Charts,Shannon-s-Dreamland/Charts,hanquochan/Charts,LiveHappier/Charts,shujucn/ios-charts,programming086/ios-charts,duanhjlt/ios-charts,icecrystal23/ios-charts,danielallsopp/Charts,danielallsopp/Charts,mobistix/ios-charts,LiveHappier/Charts,liuxuan30/Charts,boluomeng/Charts,liuxuan30/ios-charts,MAARK/Charts,noais/ios-charts,gjpc/ios-charts,jjatie/Charts,gunterhager/ios-charts,stardust139/ios-charts,SBGMobile/Charts,GreenCom-Networks/ios-charts,gjpc/ios-charts,koroff/Charts,aelam/Charts,KerryJava/ios-charts,leoMehlig/Charts,danielgindi/ios-charts,SBGMobile/Charts,hanquochan/Charts,duanhjlt/ios-charts,icecrystal23/ios-charts,summerlove57/ios-charts,leoMehlig/Charts,gunterhager/ios-charts,KerryJava/ios-charts,Eflet/Charts,MAARK/Charts,summerlove57/ios-charts,KerryJava/ios-charts,stardust139/ios-charts,jum/Charts,danielgindi/ios-charts,ConcepterDev/ios-charts,danielgindi/ios-charts