fix(vite-plugin-blocklet): fix blockletPrefix without trailingSlash cause vite error

[LancelotLewis]

Relates Issue

relates https://github.com/ArcBlock/hiring/issues/1072

Main changes

1. Fixed URL transform while URL equal to blockletPrefix

Screenshots

Check list

• Project create by create-blocklet can work with npm run dev
• Project create by create-blocklet can work with npm run deploy
• Project create by create-blocklet can work with npm run upload
• If a new version need to be publish, make sure you have run npm run bump-version command