Use later value for duplicate xref entries in PdfParser #7102
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Resolves #7084
The issue attempts to append an image to a PDF, but Pillow raises an error, "xref entry duplicated (and not identical)". This error was added in #2965 with the rest of the PDF appending functionality.
Reading https://blog.idrsolutions.com/what-are-pdf-xref-tables/ to learn more about xref tables, I found
And indeed, skipping past the duplicate value fixes the issue. We're already using the later value, because Pillow is reading the trailers in reverse order.
I created the test image using Pillow, modified the xref tables so that there is a duplicate entry with a different value, and then asserted that the later value, 1197, is used rather than the earlier value, 1196.