Fix bug when interval has span 0
Fix bug when interval has span 0

willseeyou/echarts,chenfwind/echarts,benjaminbecktg/echarts,ecomfe/echarts,benjaminbecktg/echarts,willseeyou/echarts,apache/incubator-echarts,benjaminbecktg/echarts,starlkj/echarts,100star/echarts,xiayz/echarts,starlkj/echarts,willseeyou/echarts,starlkj/echarts,chenfwind/echarts,hexj/echarts,hexj/echarts,ecomfe/echarts,xiayz/echarts,apache/incubator-echarts,hexj/echarts,100star/echarts