feature：修改连接的报错

devices/ble_manager.js

@@ -664,7 +664,9 @@ class bleManager {
           resolve(res.characteristics);
         },
         fail: (err) => {
-          that.publicDevice.characteristics = null;
+          if (that.publicDevice) {
+            that.publicDevice.characteristics = null;
+          }
           console.error('发现特征值失败:', err);
           reject("");
         }