[issue3997] zipfile and winzip

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc <amauryfa at gmail.com> added the comment:

Oops, I did see this before, but forgot to merge the patches.

It appears that "centDirOffset == 0xffffffff" is not the correct test 
for detecting zip64 structure. From the PKZip notes, a value of 
0xffffffff does imply a zip64 format, not the other way round.

So it seems necessary to always try to read the zip64 info (the _EndRecData64 function does not fail if the format is not zip64 - is 
simply returns the previous structure)
Patch is attached, and now the test passes.

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keywords: +needs review
Added file: http://bugs.python.org/file12778/zip64-alwaystry.patch

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