README rendering broken

[wxiaoguang]

https://try.gitea.io/wxiaoguang/test

[wxiaoguang]

Three related changes (RelativePath) in #19017

Maybe the first one (renderReadmeFile) should be changed back (and adding the tree path prefix?), the ctx.Repo.TreePath is empty here.

[lunny]

web/repo/view.go:366:renderReadmeFile() [E] [62abdc6e] Render failed: Render options both filename and type missing then fallback