fix: bug5727平衡表在最后一行合并单元格后无法向下插入行

src/views/datasheet_manage/components/BalanceTable.vue

@@ -1812,7 +1812,7 @@ export default {
       let startMainKey=''
       let row = new Array(this.columnHeader.length).fill("").map((_,cindex) => {
 
-        let isEnlargeCell = !!(this.config.data[index][cindex].merData && this.config.data[checkIndex][cindex] && this.config.data[checkIndex][cindex].merData)
+        let isEnlargeCell = !!(this.config.data[index][cindex].merData && (this.config.data[checkIndex]&&this.config.data[checkIndex][cindex]) && this.config.data[checkIndex][cindex].merData)
         if(isEnlargeCell && startMainKey != this.config.data[index][cindex].merData.mer.sKey){
           const data = this.config.data[index][cindex].merData.type == 'merge'?
                       this.config.data[index][cindex]: