Initialize zipcmp entries before cleanup

[soul-sol]

Summary

• initialize each populated zipcmp archive entry before assigning metadata
• prevent cleanup from freeing an indeterminate extra_fields pointer

list_zip() allocates its entry array with malloc(). In the normal non-paranoid path it sets n_extra_fields to zero but leaves extra_fields uninitialized. archive_deinit() later calls entry_deinit(), which unconditionally frees that pointer.

The existing entry_init() helper already establishes the complete ownership state, so calling it before populating an entry fixes the invalid free without changing comparison behavior.

Verification

• Before: both zipcmp_zip_dir.test and zipcmp_zip_dir_slash.test abort under ASan in archive_deinit -> entry_deinit -> free.
• After: both targeted tests pass under ASan/UBSan.
• Full ASan/UBSan regression suite: 187/187 passed.
• Existing corpus sweep: 504 runs across zip_read_fuzzer, zip_read_metadata_fuzzer, and zip_read_file_fuzzer; zero sanitizer failures.

Build flags:

CFLAGS="-O1 -g -fsanitize=address,undefined -fno-omit-frame-pointer"
LDFLAGS="-fsanitize=address,undefined"