Check for twitch preview avability before sending notification

[Satont]

Twitch can return empty image with non 200 statuscode if we requesting image to fast after stream starts. We can check this in sender service, and do incremental check on availability of image.

But we must not block main gorutines then, if we are in retrying loop.

[Satont]

/cc @danilluk1

Maybe you want to do that.