[3.14] gh-71810: Fix corner case (length==0) for int.to_bytes() (GH-138739)

[miss-islington]

>>> (0).to_bytes(0, 'big', signed=True)
b''
>>> (-1).to_bytes(0, 'big', signed=True)  # was b''
Traceback (most recent call last):
  File "<python-input-0>", line 1, in <module>
    (-1).to_bytes(0, 'big', signed=True)
    ~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
OverflowError: int too big to convert

(cherry picked from commit 011179a)

Co-authored-by: Sergey B Kirpichev [email protected]
Co-authored-by: Serhiy Storchaka [email protected]

• Issue: int.to_bytes() and int.from_bytes(): raise ValueError when bytes count is zero #71810

[vstinner]

LGTM