[Bug] Not always all new comics are displayed in slideshow

[Olf0]

Originally filed as tardypad#87.

When the slideshow to see all new comics is opened while some new comics are still being downloaded, there is an issue that the last strip(s) are 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.

A solution would be to prevent the opening of the slideshow while downloading new strips, i.e. by rendering this action in the pull down menu inactive with a text "Downloading comics".

If we continue to allow the opening the slideshow while downloading but somehow fix the final strip(s) (non-)appearance, there still is the (also) extant problem that the user just finishes "reading all new comics" but misses the ones downloaded afterwards since there is no clear indication that some additional strips are still left to be read.
Comment by olf: I do not really comprehend this last paragraph when thinking about it a bit more thoroughly. Ultimately that does not matter, because the suggested solution seems to address both (perceived) issues.