feature: 解决断开连接失败报错的问题

devices/ble_manager.js

@@ -325,9 +325,12 @@ class bleManager {
   // 断开与指定设备的连接
   disconnect() {
     var that = this;
-    let device = that.publicDevice ?? {};
-    let deviceId = device.deviceId ?? ""
-    if (deviceId.length === 0) {
+    let device = that.publicDevice;
+    if (device == null) {
+      return;
+    }
+    let deviceId = device.deviceId
+    if (deviceId == null || deviceId == "") {
       return;
     }