Fix missing return on redis parsing issues

Suggested-By: Gusted (https://codeberg.org/Codeberg/pages-server/pulls/301/files#issuecomment-1732054)

server/startup.go

@@ -84,6 +84,7 @@ func Serve(ctx *cli.Context) error {
 			opts, err := redis.ParseURL(cfg.Cache.RedisURL)
 			if err != nil {
 				redisErr = err
+				return nil
 			}
 			return cache.NewRedisCache(name, opts)
 		}