fix(bzy,scd deviceData): 修复空数据时objItem赋值异常的问题

调整监听回调的执行逻辑，当newVal为空时将objItem置为空对象，避免访问historyData[0]出现undefined的问题

pages/bzy/components/deviceData.vue

@@ -365,8 +365,10 @@ export default {
           newVal.forEach(item=>{
             this.historyData.push(item.d_h_t)
           })
+          this.objItem = this.historyData[0]
+        }else{
+          this.objItem = {}
         }
-        this.objItem = this.historyData[0]
       },
       deep:true,
       immediate:true,

pages/scd/components/deviceData.vue

@@ -363,8 +363,10 @@ export default {
           newVal.forEach(item=>{
             this.historyData.push(item.d_h_t)
           })
+          this.objItem = this.historyData[0]
+        }else{
+          this.objItem = {}
         }
-        this.objItem = this.historyData[0]
       },
       deep:true,
       immediate:true,