zip_close: check for allocation overflow and set error on failure

[filtede98]

In zip_close(), survivors is a 64-bit integer (zip_uint64_t).

1. Integer overflow prevention: On 32-bit platforms, the allocation size calculation sizeof(filelist[0]) * (size_t)survivors can wrap around size_t if survivors > SIZE_MAX / sizeof(filelist[0]). This would result in an undersized buffer allocation and subsequent out-of-bounds writes when populating ilelist[j]. We add an explicit bounds check before multiplying.
2. Missing error code on allocation failure: If malloc() failed, zip_close() previously returned -1 without setting za->error via zip_error_set(&za->error, ZIP_ER_MEMORY, 0). Callers checking zip_get_error(za) / zip_strerror(za) received a stale or uninitialized error code.
3. Empty archive handling: When survivors == 0 (e.g. keeping an empty archive with ZIP_AFL_CREATE_OR_KEEP_FILE_FOR_EMPTY_ARCHIVE), we set ilelist = NULL directly rather than invoking malloc(0), which can return NULL on some platforms/allocators and cause spurious failure.
4. qsort guard: qsort() is guarded with && survivors > 0 to avoid passing a NULL buffer pointer.

[dillof]

Thanks. The overflow can't happen because we already check that survivors < za->nentry. We applied NULL pointer handling change.