Using the part URL at closing time is really dangerous: if the user used
"save as" (e.g. for an embedded PDF), we'll be deleting the file that
the user just saved!!

BUG: 402529

launch ARK and open a ZIP file containing a PDF, click on the PDF,
an embedded viewer appears. From there, use "Save As..." to save the PDF
somewhere on your local disk. Close the embedded viewer, close ark.
It doesn't delete the saved file anymore.