Set placeholder volume

[RosaryMala]

Sometimes series that are currently being published will have a volume number set for chapters that have ben published in a volume already, while the latest chapters may not have a volume yet.
with the current behavior, chapters without a volume are automatically listed first.

It would be helpful to set a manual volume number for any chapter that doesn't have one.

[danbulant]

I think the simplest solution here would be to simply have chapter number be the first number, so it'd be saved as Ch X Vol Y in cbz. I don't think this matters to epub though.