Session should be regenerated if the session can not be found in the storage

[Spedoske]

Fiber version
2.13.0
Issue description
In most cases, unable to find session in the database indicating that the session is not valid, and the session should be regenerated.
The main idea is that we should not allow user to set an arbitrary session when the session provided by user is not in the database.

For example, we use uuid as session. While user can set a session that is not a uuid if the session string is not in the storage.

There are two main causes for the situation.

• The user provides an invalid session
• The session has expired, for example, in Redis.

Code snippet
The problems occurs here.

// middleware/session/store.go
// Get will get/create a session
func (s *Store) Get(c *fiber.Ctx) (*Session, error) {
        ...
	if loadData {
		raw, err := s.Storage.Get(id)
		// Unmashal if we found data
		if raw != nil && err == nil {
                        ...
		} else if err != nil {
			return nil, err
		} else {
			// raw is nil, which means id is not in the storage
			// so it means that id is not valid (mainly because of id is expired or user provides an invalid id)
			// therefore, we regenerate a id
			sess.fresh = true
			sess.id = s.KeyGenerator()
		}
	}

	return sess, nil
}