Don't manually replace whitespace during render

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

modules/util/url.go

@@ -25,6 +25,9 @@ func PathEscapeSegments(path string) string {
 
 // URLJoin joins url components, like path.Join, but preserving contents
 func URLJoin(base string, elems ...string) string {
+	// We do need to escape special chars here or else they can be silently discarded
+	// in the ResolveReference call below
+	base = PathEscapeSegments(base)
 	if !strings.HasSuffix(base, "/") {
 		base += "/"
 	}