don't try to interpret treepath as hash (go-gitea#17272)

...when path contains no hash-path-separator ('/')

This is a workaround to go-gitea#17179.

Entering this case when `path` does not contain a '/' does not really
make sense, as that means the tree path is empty, but this case is only
entered for routes that expect a non-empty tree path.

Treepaths like <40-char-dirname>/<filename> will still fail,
but hopefully don't occur that often. A more complete fix that avoids
this case too is outlined in go-gitea#17185, but too big of a change to backport

Author: noerw

services/context/repo.go

@@ -823,7 +823,7 @@ func getRefName(ctx *Base, repo *Repository, pathType RepoRefType) string {
 		// For legacy and API support only full commit sha
 		parts := strings.Split(path, "/")
 
-		if len(parts) > 0 && len(parts[0]) == git.ObjectFormatFromName(repo.Repository.ObjectFormatName).FullLength() {
+		if len(parts) > 1 && len(parts[0]) == git.ObjectFormatFromName(repo.Repository.ObjectFormatName).FullLength() {
 			repo.TreePath = strings.Join(parts[1:], "/")
 			return parts[0]
 		}