refactor(product-manage): 优化数据表格空值显示

- 在 competitor-monitor、product-list 和 product-monitor 组件中，对数据表格中的空值进行优化处理
- 提升用户体验

src/views/product-manage/competitor-monitor/component/DataTableSlot.vue

@@ -198,7 +198,7 @@ function starsPercent(goods: any) {
       </div>
     </div>
     <div v-else>
-      {{ row.goods[field] }}
+      {{ row.goods[field] || '-' }}
     </div>
   </div>
 </template>

src/views/product-manage/product-list/component/DataTableSlot.vue

@@ -105,7 +105,7 @@ function handleMonitor() {
       </div>
     </div>
     <div v-else>
-      {{ row[field] }}
+      {{ row[field] || '-' }}
     </div>
   </div>
 </template>

src/views/product-manage/product-monitor/component/DataTableSlot.vue

@@ -165,7 +165,7 @@ function onConfirm() {
       </div>
     </div>
     <div v-else>
-      {{ row.goods[field] }}
+      {{ row.goods[field] || '-' }}
     </div>
   </div>
 </template>