fix: Correctly compute the username from a CNAME

cmd/rio/main.go

@@ -24,8 +24,12 @@ import (
 )
 
 func handleSubdomain(domain, cname, path, giteaUrl, defaultCsp string, giteaClient *repo.GiteaClient, w http.ResponseWriter) {
-	hostParts := strings.Split(domain, ".")
-	username := hostParts[0]
+	username := ""
+	if cname != "" {
+		username = strings.Split(cname, ".")[0]
+	} else {
+		username = strings.Split(domain, ".")[0]
+	}
 
 	// Strip the leading /
 	if path[:1] == "/" {