number_pages with page filter may leave cursor on incorrect page

[pbhogan]

I have a case where I'm generating a PDF that has repeating content including repeating page numbering for each instance of the content.

So, for example:

1. Create PDF document
2. Append 4 pages
3. Call number_pages with a page_filter that excludes page 4.
4. Repeat steps 2 and 3 several times.

What happens is the 4th page in each set gets overdrawn except in the final iteration. I believe this is because number_pages calls go_to_page internally, potentially leaving the cursor on a different page from when it was called. This is unintuitive.

I was able to fix it in my case by inserting a go_to_page after every number_pages that goes to the last page in the PDF.

I believe the fix is to make number_pages return the cursor to whatever page it was on before number_pages was called.