Fix page number order.

[grinay]

For case when root nod has reference to page the order will be incorrect. The case if root node has reference [2 0 R 3 0 R 10 0 R] Where 2 0 R is intermediate node containing page 1,2,3

Where 3 0 R is intermediate node containing page 4,5,6 Where 10 0 R is page 7

without that fix 7 page will in array as page 1

[EliotJones]

Thanks for your PR I'll try and get some time to review it soon. My one worry is if it works still for this previously reported issue: https://github.com/UglyToad/PdfPig/issues/381 I don't think there was ever a test case for it but I'll double check during the review