Fix print document with zero pages backwards compatibility.

Historically, we were allowing an app that prints to specify that
the printed document has zero pages. While this does not make any
sense we should keep the behavior as people may have apps that do
that. This change fixes this issue and now we treat zero the same
way as undefined page count and ask the app to write all pages to
check the written PDF for the page count.

bug:16199127

Change-Id: I4e7de66b669e9f783db0252244a6c1e5b24ffe28