重置时，把预览图删除1

Controller/ShadowController.py

@@ -72,7 +72,10 @@ def update_device_shadow(request):
             UidSetModel.objects.filter(uid=uid).delete()
             # 重置设备，判断设备为已删除
             Device_Info.objects.filter(UID=uid).update(isExist=2)
-            UID_Preview.objects.filter(uid=uid).delete()
+            # 删除预览图
+            uid_pre_qs = UID_Preview.objects.filter(uid=uid)
+            if uid_pre_qs.exists():
+                uid_pre_qs.delete()
 
         # return JsonResponse(status=200, data={'code': 0, 'msg': 'success', 'data': {}})
         ucode = request_dict.get('ucode', None)