Partial new comics slideshow issue

[tardypad]

In case the slideshow to see all new comics is opened while some new comics are still being downloaded, there is an issue that the end panel is never displayed when all strips are read.
This is because the model still has some unread comics which are not part of the slideshow since they were downloaded after its start.

I think the best solution would be to prevent the opening of the slideshow while downloads are happening, making the action in the pull down menu inactive with a text "Downloading comics".

If we would allow the opening and somehow fix the end panel appearance, there would still be the problem left that the user just finishes "reading all new comics" and then misses the ones downloaded afterwards since there wouldn't be a clear display that some are still left to be read.