For historical reasons Gitea manually alters the urlPrefix and replaces
a whitespace with a +. This Works for URLs, but we're also passing
urlPrefix to git calls and adding the + is breaking the tree path.
Goldmark will automatically convert a white space to the proper %20, so
we should leave the string as is which lets us pass it to git unmodified
and then let Goldmark fix it.
Also fixed separate bug in URLJoin I noticed while testing where it will
silently discard sections of a path that have # in them (possibly
others). We should just escape it first.
Fixes 10156