Fixed Phalcon\Session\Flash::getMessages

[sergeyklay]

Refs #11941

[tugrul]

Better implementation:

if typeof type == "string" {
    if fetch returnMessages, messages[type] {
        if remove === true {
            unset(messages[type]);
            session->set("_flashMessages", messages);
        }
        return returnMessages;
    }

    return [];
}