当蓝牙耳机输出切换后的会有输入不可用情况时，设置默认项为空

Log: 修改蓝牙音频设备界面
Task: https://pms.uniontech.com/zentao/task-view-35808.html
Change-Id: I546811fc631564ef992aff29fbe763e2f800a746
Reviewed-on: http://gerrit.uniontech.com/c/dde-control-center/+/3195
Reviewed-by: <mailman@uniontech.com>
Reviewed-by: wangwei <wangwei@uniontech.com>
Reviewed-by: niecheng <niecheng@uniontech.com>
Tested-by: <mailman@uniontech.com>