Regression in zipfile, read1(-1) after seek() returns empty byte string

[hrnciar]

Bug report

When debugging a test failure in https://pypi.org/project/fs/ I found a regression in zipfile, read1(-1) after seek() returns empty byte string instead of substring. I've bisected it into this commit 330f1d5.

Reproducer:

import zipfile

# First, create the zip:
#   echo 'Hello, World' > hello.txt
#   zip hello.zip hello.txt

with zipfile.ZipFile('hello.zip') as myzip:
    with myzip.open('hello.txt') as myfile:
        print(myfile.read(5))
        print(myfile.seek(2, 1))
        print(myfile.read1(-1))

Expected output (3.11.2):

❯ python3.11 reproduce.py
b'Hello'
7
b'World\n'

Actual output (3.12.0a6):

❯ python3.12 reproduce.py
b'Hello'
7
b''

Your environment

• CPython versions tested on: main
• Operating system and architecture: Fedora 37, x86_64

Linked PRs

• gh-102956: Fix returning of empty byte strings after seek in zipfile … #103565
• [3.12] gh-102956: Fix returning of empty byte strings after seek in zipfile … (GH-103565) #111289

[arhadthedev]

@serhiy-storchaka, @Yhg1s, @gpshead (as zipfile experts)

[mgorny]

Ping. This is still breaking fs, and there's a patch waiting for review since April.