chore: Compatible with createRouter where basename does not start with /

[nanianlisao]

I'm not sure if this is a side effect of #8861, it works fine when I use the HashRouter parameter basename as "app1".

So I'm hoping that when I switch to createHashRouter, the basename will still support "app1", rather than requiring me to change it to "/app1".

I sincerely hope that this feature can get your approval.