fix single page mode: unnecessary rewrite from static assets to `index.html`

[littlegolden]

this pr only fix the problem that could not access static files via url directly which in Single app mode, NOT Multi Page App.

Only for reference of temporary repair.

related issues: #88, #79

BEFORE

【public & assets】

AFTER

【public & assets】

[codfish]

@vben-admin @anncwb why the hold up here? this is a massive bug and this seems to be a good fix, could we merge and publish? Otherwise this plugin is kind off unusable as it breaks Vite dev server static assets https://vitejs.dev/guide/assets.html#the-public-directory

[liuye1296]

这么严重的bug 都不给通过是放弃治疗了嘛？