Problems when page is not found

[Paulo Coutinho]

yii2-imperavi-widget/src/Widget.php

Line 202 in 0e719a3

 if (isset($this->settings['imageUpload']) && !isset($this->settings['imageUploadErrorCallback'])) { 

Problems when page is not found

When i try upload to invalid url or error 500 url, it shows a alert with message "true". Can you validate for erros 404/500 and show another message?

Thanks.

[Vasile C.]

Fixed in #108