修复ppt取消封底图后会多渲染一页的问题

src/views/ppt_manage/newVersion/components/catalog/pptContent.vue

@@ -144,7 +144,8 @@ export default {
         await this.initPageElements(this.pageList[i],'show')
       } 
       this.isLoadBack = true
-      this.loadArr.push({name:'back'})
+      if(this.pptBackImage.length)
+        this.loadArr.push({name:'back'})
 
       //获取已加载图表的信息
       let chartInfoMap = {}

src/views/ppt_manage/newVersion/components/catalog/pptContentEn.vue

@@ -140,7 +140,8 @@ export default {
         await this.initPageElements(this.pageList[i],'show')
       }
       this.isLoadBack = true
-      this.loadArr.push({name:'back'})
+      if(this.pptBackImage.length)
+        this.loadArr.push({name:'back'})
       //获取已加载图表的信息
       let chartInfoMap = {}
       for(let i=1;i<this.loadArr.length-1;i++){