Call the getctime() in a bit safer way

[SuslikV]

This is attempt to fix the issue reported on the OBS forum:
https://obsproject.com/forum/threads/help-python-script-obs-help-needed-additional-replay-buffer.157771/

It is not safe to call the os.path.getctime(path) if path is None.

Edit: I made few mistakes too, I hope it is fixed now
New code block will look like this:

def save_and_get_last_replay():
    timestamp = time.time()
    obs.obs_frontend_replay_buffer_save()

    # Try to get the file timestamp 20 times, only then give up, interval 1 sec
    for i in range(20):
        path = get_last_replay()
        if path and os.path.isfile(path):
            file_timestamp = os.path.getctime(path)
            if file_timestamp < timestamp:
                path = None
            else:
                break
        sleep(1)

    return path