Add "Skip Unlisted" button in issue selector dialog

[ArKay74]

Sometimes it happens that you have 300 books of which only 10 might be known to ComicVine (British comics mostly). So what we have to do is click "Skip" 290 times for the 10 issues that are known to get scraped. It would be nice if there was a "Skip Unlisted" button that wouldn't ask for an issue number when the issue isn't in the list (why bother asking if it's not there?)

I realize that it's a rare use case, but it shouldn't be too difficult to implement and saves a lot of clicking when it happens.