微信公众号扫描带参数二维码事件，首次扫码关注公众号推送的EventKey为空，但关注后再扫就正常

关注事件：

<xml><ToUserName><![CDATA[gh_e9e5d7970549]]></ToUserName>

<FromUserName><![CDATA[owhj-6TkcqkNAmSDZCFQNhntmHF8]]></FromUserName>

<CreateTime>1737597034</CreateTime>

<MsgType><![CDATA[event]]></MsgType>

<Event><![CDATA[subscribe]]></Event>

<EventKey><![CDATA[]]></EventKey>

</xml>

关注后在扫码就正常：

<xml><ToUserName><![CDATA[gh_e9e5d7970549]]></ToUserName>

<FromUserName><![CDATA[owhj-6TkcqkNAmSDZCFQNhntmHF8]]></FromUserName>

<CreateTime>1737596238</CreateTime>

<MsgType><![CDATA[event]]></MsgType>

<Event><![CDATA[SCAN]]></Event>

<EventKey><![CDATA[2]]></EventKey>

<Ticket><![CDATA[gQEk8jwAAAAAAAAAAS5odHRwOi8vd2VpeGluLnFxLmNvbS9xLzAybldvdWQwMm9mLUYxMDAwMDAwMzUAAgTutYtnAwQAAAAA]]></Ticket>

</xml>