archive/zip: non-standard handling of conflicts between central directory and local file headers

[neild]

This is related to #40354, but a bit different.

Construct a zip file containing a file where:

• The central directory record contains a compressed file size of S1.
• The local file header gives a contains a compressed file size of 0.
• Bit 3 of the local file header's flag bit is 0.

Info-Zip's UnZip will prefer the local file header (extracting a file of size 0), but archive/zip will prefer the central directory record (extracting S1 compressed bytes).

PKWARE's spec says about bit 3 of the local file header flags:

         Bit 3: If this bit is set, the fields crc-32, compressed 
               size and uncompressed size are set to zero in the 
               local header.  The correct values are put in the 
               data descriptor immediately following the compressed
               data.  (Note: PKZIP version 2.04g for DOS only 
               recognizes this bit for method 8 compression, newer 
               versions of PKZIP recognize this bit for any 
               compression method.)

I haven't attempted to check what other implementations do. (Actually, I'm not sure if bit 3 is relevant or not here, but the spec seems to indicate that it is.)

[dsnet]

In the event of obvious inconsistency between the central and local headers, do we report an error?

[neild]

In the event of obvious inconsistency between the central and local headers, do we report an error?

Not currently. We seem to just ignore the local headers entirely.

Reporting an error if there's a mismatch seems reasonable.