perf(views): 优化“设备工况”模块参数的历史数据曲线

1. tooltip 显示时，若值为空，则替换为 -

src/views/device-work-status/DevWorkParamData.vue

@@ -143,7 +143,7 @@ const option = computed<EChartsOption>(() => {
         tableHtml += `<tr><th>${time}</th></tr>`;
 
         tempParms.forEach((param) => {
-          tableHtml += `<tr><td>${param.marker}${param.seriesName}</td><td>${param.value[1]}${unitText}</td></tr>`;
+          tableHtml += `<tr><td>${param.marker}${param.seriesName}</td><td>${param.value[1] ?? '-'}${unitText}</td></tr>`;
         });
 
         tableHtml += '</table>';